public virtual ExportedDocument ExportDocumentStarting(
    string documentId,
    string asyncExportOperationId,
    string format,
    ExportOptions options,
    PrintingSystemBase printingSystem,
    Func<ExportedDocument> doExportSynchronously
)

Public Overridable Function ExportDocumentStarting(
    documentId As String,
    asyncExportOperationId As String,
    format As String,
    options As ExportOptions,
    printingSystem As PrintingSystemBase,
    doExportSynchronously As Func(Of ExportedDocument)
) As ExportedDocument

using DevExpress.XtraPrinting;
using DevExpress.XtraReports.UI;
using DevExpress.XtraReports.Web.ClientControls;
using DevExpress.XtraReports.Web.WebDocumentViewer;
using System;
using System.IO;

public class MyOperationLogger : WebDocumentViewerOperationLogger
{
    public override ExportedDocument ExportDocumentStarting(string documentId, 
    string asyncExportOperationId, string format, ExportOptions options, 
    PrintingSystemBase printingSystem, Func<ExportedDocument> doExportSynchronously)
    {
        switch (format)
        {
            case "pdf":
                {
                    // Creates a one-page NEW report.
                    var report = new XtraReport();
                    var detail = new DetailBand();
                    detail.Controls.Add(new XRLabel() { Text = "Hello World!" });
                    report.Bands.Add(detail);
                    byte[] bytes;
                    using (MemoryStream ms = new MemoryStream())
                    {
                        report.ExportToPdf(ms, options.Pdf);
                        bytes = ms.ToArray();
                    }
                    return new ExportedDocument(bytes, @"application/pdf", "inline", "SampleOnePageReport.pdf");
                }
            case "xls":
            case "xlsx":
                {
                    // Modifies an existing report.
                    var report = new TestReport();
                    XRTable table = report.FindControl("table3", true) as XRTable;
                    table.BackColor = System.Drawing.Color.LightGreen;
                    byte[] bytes;
                    using (MemoryStream ms = new MemoryStream())
                    {
                        report.ExportToXlsx(ms, options.Xlsx);
                        bytes = ms.ToArray();
                    }
                    return new ExportedDocument(bytes, @"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", "inline", "SampleGreenCells.xlsx");
                }
            default: return base.ExportDocumentStarting(documentId, 
            asyncExportOperationId, format, options, printingSystem, doExportSynchronously);
        }
    }
}

function onCustomizeMenu(s, e) {
        var actionExportTo = e.GetById(DevExpress.Reporting.Viewer.ActionId.ExportTo);
        actionExportTo.items()[0].items.push({
            format: "JPEG",
            text: "Image: JPEG",
        });
}

'use client';
import React from 'react';
import ReportViewer, { RequestOptions, Callbacks } from 'devexpress-reporting-react/dx-report-viewer';
import { ActionId } from "devexpress-reporting/viewer/constants";

const App = () => {
  const onCustomizeMenuActions = (event: any): void => {
    const actionExportTo = event.args.GetById(ActionId.ExportTo);
    const newFormat = { format: 'JPEG', text: 'Image: JPEG' };
    if (actionExportTo) {
      actionExportTo.events.on('propertyChanged', (args: any) => {
        const formats = actionExportTo.items[0].items;
        if (args.propertyName === 'items' && formats.indexOf(newFormat) === -1) {
          formats.push(newFormat);
        }
      });
    }
  };

  return (
    <ReportViewer reportUrl="TestExportReport">
      <RequestOptions host="http://localhost:5000/" invokeAction="DXXRDV" />
      <Callbacks CustomizeMenuActions={onCustomizeMenuActions} />
    </ReportViewer>
  );
};

export default App;

using DevExpress.XtraPrinting;
using DevExpress.XtraReports.UI;
using DevExpress.XtraReports.Web.ClientControls;
using DevExpress.XtraReports.Web.WebDocumentViewer;
using System;
using System.Drawing.Imaging;
using System.IO;

public class MyOperationLogger : WebDocumentViewerOperationLogger
{
    public override ExportedDocument ExportDocumentStarting(string documentId, 
    string asyncExportOperationId, string format, ExportOptions options, 
    PrintingSystemBase printingSystem, Func<ExportedDocument> doExportSynchronously)
    {
        switch (format)
        {
            case "JPEG":
                {
                    var report = new TestReport();
                    byte[] bytes;
                    using (MemoryStream ms = new MemoryStream())
                    {
                        report.ExportToImage(ms,
                            new ImageExportOptions()
                            {
                                Format = ImageFormat.Jpeg,
                                ExportMode = ImageExportMode.SingleFilePageByPage,
                                PageRange = "1"
                            });
                        bytes = ms.ToArray();
                    }
                    return new ExportedDocument(bytes, @"image/jpeg", "inline", "SampleImage.jpeg");
                }
            default: return base.ExportDocumentStarting(documentId, 
            asyncExportOperationId, format, options, printingSystem, doExportSynchronously);
        }
    }
}

using DevExpress.Spreadsheet;
using DevExpress.XtraPrinting;
using DevExpress.XtraReports.Web.ClientControls;
using DevExpress.XtraReports.Web.WebDocumentViewer;
using System;
using System.IO;

public class MyOperationLogger : WebDocumentViewerOperationLogger
{
    public override ExportedDocument ExportDocumentStarting(string documentId, 
        string asyncExportOperationId, string format, 
        ExportOptions options, PrintingSystemBase printingSystem, 
        Func<ExportedDocument> doExportSynchronously)
    {
        // ...
        if (format == "xls" || format == "xlsx")
        {
            // Calls the default Export procedure.
            ExportedDocument document = doExportSynchronously();

            // Transforms the exported document to a Workbook class instance.  
            IWorkbook workbook = new Workbook();
            workbook.LoadDocument(document.Bytes);
            Worksheet worksheet = workbook.Worksheets[0];

            // Gets the username.  
            string author = workbook.CurrentAuthor;

            // Adds a comment to the A1 cell.  
            Cell cell = worksheet.Cells["A1"];
            Comment comment = worksheet.Comments.Add(cell, author, 
                "This is important information for users.");

            // Adds a user name to beginning of the comment.  
            CommentRunCollection runs = comment.Runs;
            runs.Insert(0, author + ": \r\n");
            runs[0].Font.Bold = true;

            // Formats the comment text.  
            runs[1].Font.Color = System.Drawing.Color.Red;
            runs[1].Font.Name = "Times New Roman";
            runs[1].Font.Size = 14;
            runs[1].Font.Italic = true;

            // Adds a new comment to the document collection of 'runs'.  
            runs.Add("\n Never delete this comment!");
            runs[2].Font.Color = System.Drawing.Color.MidnightBlue;

            // Saves the modified document.  
            MemoryStream ms = new MemoryStream();
            workbook.SaveDocument(ms, (format == "xls") ? DocumentFormat.Xls : DocumentFormat.Xlsx);
            document.Bytes = ms.ToArray();
            return document;
        }
        return base.ExportDocumentStarting(documentId, 
            asyncExportOperationId, format, options, 
            printingSystem, doExportSynchronously);
    }
}

SaveUsedEntityId(Constants.ExportedDocumentDictionaryName, asyncExportOperationId);
return base.ExportDocumentStarting(documentId, asyncExportOperationId, format, options,
    printingSystem, doExportSynchronously);

SaveUsedEntityId(Constants.ExportedDocumentDictionaryName, asyncExportOperationId)
Return MyBase.ExportDocumentStarting(documentId, asyncExportOperationId, format,
                                     options, printingSystem, doExportSynchronously)