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Overview

OnlyOffice Document Server provides three specialized editors for different document types:
  • Word Processor - Text documents
  • Spreadsheet - Workbooks and data tables
  • Presentation - Slide decks
The OnlyOffice Control library automatically detects the document type based on file extension and loads the appropriate editor.

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Supported Formats

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Word Processor Documents (word)

The word processor handles text documents and is the default editor.
FormatExtensionDescription
Microsoft Word.doc, .docxModern and legacy Word formats
OpenDocument Text.odtOpen standard text format
Rich Text Format.rtfCross-platform rich text
Plain Text.txtUnformatted text files
The word processor is used as the fallback for any unrecognized file types.

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Spreadsheet Documents (cell)

The spreadsheet editor handles workbooks with formulas, charts, and data analysis.
FormatExtensionDescription
Microsoft Excel.xls, .xlsxModern and legacy Excel formats
OpenDocument Spreadsheet.odsOpen standard spreadsheet format
Comma-Separated Values.csvPlain text data tables

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Presentation Documents (slide)

The presentation editor handles slide decks with multimedia and transitions.
FormatExtensionDescription
Microsoft PowerPoint.ppt, .pptxModern and legacy PowerPoint formats
OpenDocument Presentation.odpOpen standard presentation format

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Document Type Resolution

The library uses the ResolveDocumentType method to map file extensions to OnlyOffice editor types:
OnlyOfficeEditor.ascx.cs:411-427
private static string ResolveDocumentType(string fileType)
{
    switch ((fileType ?? "").ToLowerInvariant())
    {
        case "xls":
        case "xlsx":
        case "ods":
        case "csv":
            return "cell";
        case "ppt":
        case "pptx":
        case "odp":
            return "slide";
        default:
            return "word";
    }
}
  1. Extracts file extension from DocumentName
  2. Converts extension to lowercase for case-insensitive matching
  3. Returns the appropriate OnlyOffice document type identifier:
    • cell for spreadsheets
    • slide for presentations
    • word for text documents (default)
  4. Includes the type in the editor configuration JSON

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Document Type in Configuration

The resolved document type is included in the editor initialization configuration:
OnlyOfficeEditor.ascx.cs:263-296
private string BuildConfigJson()
{
    var ext = Path.GetExtension(DocumentName);
    var fileType = string.IsNullOrWhiteSpace(ext) ? "" : ext.TrimStart('.');

    var config = new
    {
        document = new
        {
            fileType,  // Raw extension ("docx", "xlsx", etc.)
            key = DocumentKey,
            title = DocumentName,
            url = DocumentUrl
        },
        documentType = ResolveDocumentType(fileType),  // Editor type ("word", "cell", "slide")
        editorConfig = new
        {
            callbackUrl = CallbackUrl ?? "",
            mode = Mode ?? "edit",
            lang = Lang ?? "es",
            user = new { id = UserId ?? "1", name = UserDisplayName ?? "Usuario" }
        }
    };
    
    // ... JWT token creation
}

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Format Compatibility

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Read and Edit Support

Most formats support both reading and editing: 
// Edit a Word document
docEditor.SetDocumentFromFile("report.docx");
docEditor.Mode = "edit";

// Edit an Excel spreadsheet
docEditor.SetDocumentFromFile("budget.xlsx");

// Edit a PowerPoint presentation
docEditor.SetDocumentFromFile("slides.pptx");

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View-Only Mode

Some formats or scenarios may require view-only access: 
docEditor.SetDocumentFromFile("contract.pdf");
docEditor.Mode = "view";  // Read-only mode

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Legacy Format Limitations

Legacy Format Considerations:
  • .doc, .xls, .ppt files may have limited feature support
  • Complex formatting might not fully preserve during editing
  • Consider converting legacy formats to modern formats (.docx, .xlsx, .pptx) for best results

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Document Conversion

The library supports converting documents to PDF regardless of the source format:
OnlyOfficeEditor.ascx.cs:163-207
private string ConvertDocumentSourceToPdfUrl(string sourceUrl, string sourceName, string sourceKey, int maxAttempts, int delayMs)
{
    // Extract extension for conversion service
    var sourceExt = Path.GetExtension(sourceName)?.TrimStart('.').ToLowerInvariant();
    if (string.IsNullOrWhiteSpace(sourceExt))
        throw new InvalidOperationException("No fue posible determinar el tipo del documento.");

    var convertServiceUrl = ResolveConvertServiceUrl();
    var serializer = new JavaScriptSerializer();
    
    var requestPayload = new Dictionary<string, object>
    {
        ["async"] = false,
        ["filetype"] = sourceExt,  // Source format
        ["outputtype"] = "pdf",    // Target format
        ["url"] = sourceUrl,
        ["title"] = Path.GetFileName(sourceName),
        ["key"] = sourceKey
    };
    
    // ... JWT signing and API call
}

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Supported Conversion Sources

All supported document types can be converted to PDF: 
// Convert Word to PDF
docEditor.SetDocumentFromFile("document.docx");
var pdfBytes = docEditor.ConvertCurrentDocumentToPdfBytes();

// Convert Excel to PDF
docEditor.SetDocumentFromFile("spreadsheet.xlsx");
var pdfUrl = docEditor.ConvertCurrentDocumentToPdfUrl();

// Convert PowerPoint to PDF
docEditor.SetDocumentFromFile("presentation.pptx");
var pdfBytes = docEditor.ConvertEditedDocumentToPdfBytes();

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Adding Custom Format Support

To extend support for additional formats, modify the ResolveDocumentType method: 
private static string ResolveDocumentType(string fileType)
{
    switch ((fileType ?? "").ToLowerInvariant())
    {
        // Spreadsheets
        case "xls":
        case "xlsx":
        case "ods":
        case "csv":
        case "xlsm":  // Add macro-enabled Excel
            return "cell";
        
        // Presentations
        case "ppt":
        case "pptx":
        case "odp":
        case "pptm":  // Add macro-enabled PowerPoint
            return "slide";
        
        // Word documents (default)
        default:
            return "word";
    }
}
Ensure the OnlyOffice Document Server supports any custom formats you add. Check the OnlyOffice format compatibility matrix for details.

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File Extension Detection

The library extracts file extensions in the configuration builder:
OnlyOfficeEditor.ascx.cs:265-266
var ext = Path.GetExtension(DocumentName);
var fileType = string.IsNullOrWhiteSpace(ext) ? "" : ext.TrimStart('.');

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Handling Missing Extensions

If no extension is detected:
  • The fileType is set to an empty string
  • ResolveDocumentType returns "word" (default fallback)
  • OnlyOffice attempts to open the file with the word processor
// Without extension - defaults to word processor
docEditor.DocumentName = "MyDocument";  // No extension
docEditor.DocumentUrl = "https://example.com/download/file123";
Always include file extensions in DocumentName for proper editor selection:
// Good
docEditor.SetDocumentFromBytes(data, "report.xlsx");

// Bad - may open with wrong editor
docEditor.SetDocumentFromBytes(data, "report");

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Example: Working with Different Document Types

protected void LoadDocument(string filePath)
{
    var ext = Path.GetExtension(filePath).ToLowerInvariant();
    
    docEditor.SetDocumentFromFile(filePath);
    
    // Configure based on document type
    switch (ext)
    {
        case ".xlsx":
        case ".xls":
            docEditor.EditorHeight = "700px";  // More height for spreadsheets
            lblDocType.Text = "Spreadsheet Editor";
            break;
            
        case ".pptx":
        case ".ppt":
            docEditor.EditorHeight = "600px";  // Presentation aspect ratio
            lblDocType.Text = "Presentation Editor";
            break;
            
        default:
            docEditor.EditorHeight = "520px";  // Standard document height
            lblDocType.Text = "Document Editor";
            break;
    }
}

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Troubleshooting Format Issues

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Wrong Editor Opens

Symptom: Excel file opens in Word editor Solution: Verify the file extension is properly set: 
// Check the DocumentName property
System.Diagnostics.Debug.WriteLine("Document: " + docEditor.DocumentName);
System.Diagnostics.Debug.WriteLine("Extension: " + Path.GetExtension(docEditor.DocumentName));

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Format Not Supported Error

Symptom: OnlyOffice shows “Format not supported” error Possible Causes:
  1. File extension not recognized by OnlyOffice
  2. File is corrupted or not actually the claimed format
  3. OnlyOffice Document Server doesn’t have format support installed
Solution: Verify file integrity and OnlyOffice server configuration

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Conversion Failures

Symptom: PDF conversion fails for specific formats Solution: Check OnlyOffice conversion service logs: 
sudo tail -f /var/log/onlyoffice/documentserver/converter/out.log

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