update :

I implemented this :

using System;

using System.Collections.Generic; using System.IO; using System.IO.Compression; using System.Linq; using System.Text; using System.Threading.Tasks; using Umbraco.Core; using Umbraco.Core.IO; using Umbraco.Core.Logging; using Umbraco.Core.Services; using Umbraco.Forms; using Umbraco.Forms.Core; using Umbraco.Forms.Core.Models; using Umbraco.Forms.Core.Enums; using Umbraco.Forms.Data.Storage; using Umbraco.Core.Persistence; using System.Globalization; using Umbraco.Forms.Core.Searchers; using Umbraco.Forms.Core.Persistence.Dtos; using Umbraco.Forms.Core.Interfaces; using Umbraco.Core.Scoping; using System.Data; using Newtonsoft.Json; using Umbraco.Core.Models; using NPoco; using Umbraco.Forms.Core.Services; using Umbraco.Web; using Umbraco.Forms.Core.Data.Storage;

namespace UmbracoPDFexport { public class _formRecordSearcher : IFormRecordSearcher { private readonly IFieldTypeStorage _fieldTypeStorage; private readonly IFormStorage _formStorage; private readonly ILocalizedTextService _localizedTextService; private readonly IMemberService _memberService; private readonly IScopeProvider _scopeProvider; private readonly IUmbracoContextAccessor _umbracoContextAccessor;

    public global::NPoco.Sql BuildSqlQuery(IScope scope, RecordFilter model, string select = "")
    {
        throw new NotImplementedException();
    }

    //public EntrySearchResultCollection QueryDataBase(RecordFilter model)
    //{
    //    throw new NotImplementedException();
    //}
    public EntrySearchResultCollection QueryDataBase(RecordFilter model) => this.QueryDataBaseForSubmissions(model, true);

    private EntrySearchResultCollection QueryDataBaseForSubmissions(RecordFilter model, bool enforceSensitiveData = true)
    {
        bool? scopeFileSystems = null;
        using (IScope scope = this._scopeProvider.CreateScope(IsolationLevel.Unspecified, RepositoryCacheMode.Unspecified, null, scopeFileSystems, false, false))
        {
            bool flag = this._umbracoContextAccessor.UmbracoContext.Security.CurrentUser.HasAccessToSensitiveData();
            Form form = this._formStorage.GetForm(model.Form);
            Sql sql = this.BuildSqlQuery(scope, model, "");
            Page<Record> page = scope.Database.Page<Record>((long)model.StartIndex, (long)model.Length, sql);
            EntrySearchResultCollection collection1 = new EntrySearchResultCollection();
            collection1.TotalNumberOfResults = page.TotalItems;
            collection1.TotalNumberOfPages = page.TotalPages;
            EntrySearchResultCollection results = collection1;
            //bool flag2 = Configuration.IsTrial && !Licensing.IsLocalBrowserRequest();
            List<EntrySearchResult> list = new List<EntrySearchResult>();
            if (form != null)
            {
                List<EntrySearchResultSchema> list2 = new List<EntrySearchResultSchema>();
                foreach (Field field in form.AllFields)
                {
                    FieldType fieldTypeByField = this._fieldTypeStorage.GetFieldTypeByField(field);
                    if (fieldTypeByField.StoresData)
                    {
                        EntrySearchResultSchema schema1 = new EntrySearchResultSchema();
                        schema1.Name = field.Caption;
                        schema1.Id = field.Id.ToString();
                        schema1.View = fieldTypeByField.RenderView;
                        EntrySearchResultSchema schema = schema1;
                        if (field.ContainsSensitiveData)
                        {
                            schema.ContainsSensitiveData = true;
                        }
                        list2.Add(schema);
                    }
                }
                EntrySearchResultSchema item = new EntrySearchResultSchema();
                item.Id = "member";
                item.View = "member";
                item.Name = "Member";
                item.ContainsSensitiveData = true;
                list2.Add(item);
                EntrySearchResultSchema schema4 = new EntrySearchResultSchema();
                schema4.Id = "state";
                schema4.View = "text";
                schema4.Name = "State";
                list2.Add(schema4);
                EntrySearchResultSchema schema5 = new EntrySearchResultSchema();
                schema5.Id = "created";
                schema5.View = "date";
                schema5.Name = "Created";
                list2.Add(schema5);
                EntrySearchResultSchema schema6 = new EntrySearchResultSchema();
                schema6.Id = "updated";
                schema6.View = "date";
                schema6.Name = "Updated";
                list2.Add(schema6);
                results.schema = list2;
            }
            foreach (Record record in page.Items)
            {
                EntrySearchResult result1 = new EntrySearchResult();
                result1.Id = record.Id;
                result1.Form = record.Form.ToString();
                result1.State = record.StateAsString;
                EntrySearchResult item = result1;
                int num = -model.LocalTimeOffset;
                DateTimeOffset now = DateTimeOffset.Now;
                TimeSpan offset = now.Offset;
                int num2 = Convert.ToInt32(offset.TotalMinutes);
                int num3 = num - num2;
                item.Created = record.Created.AddMinutes((double)num3);
                item.Updated = record.Updated.AddMinutes((double)num3);
                item.UniqueId = record.UniqueId;
                try
                {
                    if (!string.IsNullOrEmpty(record.MemberKey))
                    {
                        IMember byId = this._memberService.GetById(Convert.ToInt32(record.MemberKey));
                        if (byId != null)
                        {
                            item.Member = byId;
                        }
                    }
                }
                catch (Exception ex)
                {

                    //do nothing
                }
                if ((form != null) && !string.IsNullOrEmpty(record.RecordData))
                {
                    Dictionary<string, string> dictionary = JsonConvert.DeserializeObject<Dictionary<string, string>>(record.RecordData);
                    List<object> list3 = new List<object>();
                    string str = _localizedTextService.Localize("content/isSensitiveValue", CultureInfo.CurrentCulture, null);
                    foreach (EntrySearchResultSchema schema2 in results.schema.Take<EntrySearchResultSchema>(results.schema.Count<EntrySearchResultSchema>() - 4))
                    {
                        if (!dictionary.ContainsKey(schema2.Id))
                        {
                            list3.Add(string.Empty);
                            continue;
                        }
                        //if (flag2)
                        //{
                        //    list3.Add(Configuration.TrialSaveMessage);
                        //    continue;
                        //}
                        if ((flag || !schema2.ContainsSensitiveData) ? (enforceSensitiveData && schema2.ContainsSensitiveData) : true)
                        {
                            list3.Add(str);
                            continue;
                        }
                        list3.Add(dictionary[schema2.Id]);
                    }
                    try
                    {
                        list3.Add(item.Member);
                    }
                    catch (Exception ex)
                    {

                       //do nothing
                    }
                    list3.Add(item.State);
                    list3.Add(item.Created);
                    list3.Add(item.Updated);
                    item.Fields = list3;
                }
                list.Add(item);
            }
            results.Results = list;
            scope.Complete();
            return results;
        }
    }
}
public class ExportToTextFile : ExportType
{
    public ExportToTextFile()
    {
        this.Name = "Export as pdf files";
        this.Description = "Export entries as pdf files inside a zip file";
        this.Id = new Guid("171CABC9-2207-4575-83D5-2A77E824D5DB");
        this.FileExtension = "zip";
        this.Icon = "icon-zip";
    }

    /// <summary>
    /// We do not implement this method from the interface
    /// As this method is called from ExportToFile that we also override here & is expecting the file contents as a string to be written as a stream to a file
    /// Which would be OK if we were creating a CSV or a single based file that can have a simple string written as a string such as one large HTML report or XML file perhaps
    /// </summary>

    public override string ExportRecords(RecordExportFilter filter)
    {
        throw new NotImplementedException();
    }

    /// <summary>
    /// This gives us greater control of the export process
    /// </summary>
    /// <param name="filter">
    /// This filter contains the date range & other search parameters to limit the entries we are exporting
    /// </param>
    /// <param name="filepath">
    /// The filepath that the export file is expecting to be served from
    /// So ensure that the zip of text files is saved at this location
    /// </param>
    /// <returns>The final file path to serve up as the export - this is unlikely to change through the export logic</returns>
    public override string ExportToFile(RecordExportFilter filter, string filepath)
    {
        // Before Save - Check Path, Directory & Previous File export does not exist
        string pathToSaveZipFile = filepath;

        // Check our path does not contain \\
        // If not, use the filePath
        if (filepath.Contains('\\') == false)
        {
            pathToSaveZipFile = IOHelper.MapPath(filepath);
        }

        // Get the directory (strip out \\ if it exists)
        var dir = filepath.Substring(0, filepath.LastIndexOf('\\'));
        var tempFileDir = Path.Combine(dir, "text-files");


        // If the path does not end with our file extension, ensure it's added
        if (pathToSaveZipFile.EndsWith("." + FileExtension) == false)
        {
            pathToSaveZipFile += "." + FileExtension;
        }

        // Check that the directory where we will save the ZIP file temporarily exists
        // If not just create it
        if (Directory.Exists(tempFileDir) == false)
        {
            Directory.CreateDirectory(tempFileDir);
        }

        // Check if the zip file exists already - if so delete it, as we have a new update
        if (System.IO.File.Exists(pathToSaveZipFile))
        {
            System.IO.File.Delete(pathToSaveZipFile);
        }


        // Query the DB for submissions to export based on the filter

        _formRecordSearcher recordSearcher = new _formRecordSearcher();
        EntrySearchResultCollection submissions = recordSearcher.QueryDataBase(filter);

        // Get the schema objects to a list so we can get items using position index
        var schemaItems = submissions.schema.ToList();

        // We will use this to store our contents of our file to save as a text file
        var fileContents = string.Empty;

        // For each submission we have build up a string to save to a text file
        foreach (var submission in submissions.Results)
        {
            // The submitted data for the form submission
            var submissionData = submission.Fields.ToList();

            // For loop to match the schema position to the submission data
            for (int i = 0; i < schemaItems.Count; i++)
            {
                // Concat a string of the name of the field & its stored data
                fileContents += schemaItems[i].Name + ": " + submissionData[i] + Environment.NewLine;
            }

            // Now save the contents to a text file
            // Base it on the format of the record submission unique id
            var textFileName = Path.Combine(tempFileDir, submission.UniqueId + ".pdf");
            System.IO.File.WriteAllText(textFileName, fileContents);

            // Reset fileContents to be empty again
            fileContents = string.Empty;
        }

        // Now we have a temp folder full of text files
        // Generate a zip file containing them & save that
        ZipFile.CreateFromDirectory(tempFileDir, pathToSaveZipFile);

        // Tidy up after ourselves & delete the temp folder of text files
        if (Directory.Exists(tempFileDir))
        {
            Directory.Delete(tempFileDir, true);
        }

        // Return the path where we saved the zip file containing the text files
        return pathToSaveZipFile;
    }

}

and it is giving me a weird error :

Possibly unhandled rejection: {"data":{"Message":"An error has occurred.","ExceptionMessage":"Object reference not set to an instance of an object.","ExceptionType":"System.NullReferenceException","StackTrace":"   at UmbracoPDFexport._formRecordSearcher.QueryDataBaseForSubmissions(RecordFilter model, Boolean enforceSensitiveData)\r\n   at UmbracoPDFexport._formRecordSearcher.QueryDataBase(RecordFilter model)\r\n   at UmbracoPDFexport.ExportToTextFile.ExportToFile(RecordExportFilter filter, String filepath)\r\n   at Umbraco.Forms.Web.Editors.ExportController.PostGenerateExport(RecordExportFilter model)\r\n   at lambda_method(Closure , Object , Object[] )\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass6_2.<GetExecutor>b__2(Object instance, Object[] methodParameters)\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.Execute(Object instance, Object[] arguments)\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__6.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__15.MoveNext()"},"status":500,"config":{"method":"POST","transformRequest":[null],"transformResponse":[null],"jsonpCallbackParam":"callback","url":"backoffice/UmbracoForms/Export/PostGenerateExport","data":{"startIndex":1,"length":20,"form":"b2413bd7-54f0-46eb-a7ad-0fde030638f1","sortBy":"created","sortOrder":"descending","states":["Approved","Submitted"],"localTimeOffset":-120,"exportType":"171cabc9-2207-4575-83d5-2a77e824d5db"},"headers":{"Accept":"application/json, text/plain, */*","Content-Type":"application/json;charset=utf-8","X-Requested-With":"XMLHttpRequest","X-UMB-XSRF-TOKEN":"BZoVuqZZ8PZ4WL-xVe57KWIHU1cQR8u33G9G0PPFD-P4zmp6jbK9N2k1I6dC4KfJ74kYl6mPIhXCO-bnvpWy5HlWSH2Pu0CbgmbkEp4XRd9bq1XW3jN4SsMSmBVMgf2yCZCihMUAFknk-HEXWgn20Q2"}},"statusText":"","xhrStatus":"complete"}

does anyone have any idea what is this?

thank you.

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