IWarningCallback interface

Implement this interface if you want to have your own custom method called to capture loss of fidelity warnings that can occur during document loading or saving.

public interface IWarningCallback


Warning(WarningInfo)Aspose.Words invokes this method when it encounters some issue during document loading or saving that might result in loss of formatting or data fidelity.


Shows how to use the IWarningCallback interface to monitor font substitution warnings.

public void SubstitutionWarning()
    Document doc = new Document();
    DocumentBuilder builder = new DocumentBuilder(doc);

    builder.Font.Name = "Times New Roman";
    builder.Writeln("Hello world!");

    FontSubstitutionWarningCollector callback = new FontSubstitutionWarningCollector();
    doc.WarningCallback = callback;

    // Store the current collection of font sources, which will be the default font source for every document
    // for which we do not specify a different font source.
    FontSourceBase[] originalFontSources = FontSettings.DefaultInstance.GetFontsSources();

    // For testing purposes, we will set Aspose.Words to look for fonts only in a folder that does not exist.
    FontSettings.DefaultInstance.SetFontsFolder(string.Empty, false);

    // When rendering the document, there will be no place to find the "Times New Roman" font.
    // This will cause a font substitution warning, which our callback will detect.
    doc.Save(ArtifactsDir + "FontSettings.SubstitutionWarning.pdf");


    Assert.True(callback.FontSubstitutionWarnings[0].WarningType == WarningType.FontSubstitution);
            "Font 'Times New Roman' has not been found. Using 'Fanwood' font instead. Reason: first available font.", StringComparison.Ordinal));

private class FontSubstitutionWarningCollector : IWarningCallback
    /// <summary>
    /// Called every time a warning occurs during loading/saving.
    /// </summary>
    public void Warning(WarningInfo info)
        if (info.WarningType == WarningType.FontSubstitution)

    public WarningInfoCollection FontSubstitutionWarnings = new WarningInfoCollection();

Shows added a fallback to bitmap rendering and changing type of warnings about unsupported metafile records.

public void HandleBinaryRasterWarnings()
    Document doc = new Document(MyDir + "WMF with image.docx");

    MetafileRenderingOptions metafileRenderingOptions = new MetafileRenderingOptions();

    // Set the "EmulateRasterOperations" property to "false" to fall back to bitmap when
    // it encounters a metafile, which will require raster operations to render in the output PDF.
    metafileRenderingOptions.EmulateRasterOperations = false;

    // Set the "RenderingMode" property to "VectorWithFallback" to try to render every metafile using vector graphics.
    metafileRenderingOptions.RenderingMode = MetafileRenderingMode.VectorWithFallback;

    // Create a "PdfSaveOptions" object that we can pass to the document's "Save" method
    // to modify how that method converts the document to .PDF and applies the configuration
    // in our MetafileRenderingOptions object to the saving operation.
    PdfSaveOptions saveOptions = new PdfSaveOptions();
    saveOptions.MetafileRenderingOptions = metafileRenderingOptions;

    HandleDocumentWarnings callback = new HandleDocumentWarnings();
    doc.WarningCallback = callback;

    doc.Save(ArtifactsDir + "PdfSaveOptions.HandleBinaryRasterWarnings.pdf", saveOptions);

    Assert.AreEqual(1, callback.Warnings.Count);
    Assert.AreEqual("'R2_XORPEN' binary raster operation is not supported.",

/// <summary>
/// Prints and collects formatting loss-related warnings that occur upon saving a document.
/// </summary>
public class HandleDocumentWarnings : IWarningCallback
    public void Warning(WarningInfo info)
        if (info.WarningType == WarningType.MinorFormattingLoss)
            Console.WriteLine("Unsupported operation: " + info.Description);

    public WarningInfoCollection Warnings = new WarningInfoCollection();

Shows how to set the property for finding the closest match for a missing font from the available font sources.

public void EnableFontSubstitution()
    // Open a document that contains text formatted with a font that does not exist in any of our font sources.
    Document doc = new Document(MyDir + "Missing font.docx");

    // Assign a callback for handling font substitution warnings.
    HandleDocumentSubstitutionWarnings substitutionWarningHandler = new HandleDocumentSubstitutionWarnings();
    doc.WarningCallback = substitutionWarningHandler;

    // Set a default font name and enable font substitution.
    FontSettings fontSettings = new FontSettings();
    fontSettings.SubstitutionSettings.DefaultFontSubstitution.DefaultFontName = "Arial";
    fontSettings.SubstitutionSettings.FontInfoSubstitution.Enabled = true;

    // Original font metrics should be used after font substitution.
    doc.LayoutOptions.KeepOriginalFontMetrics = true;

    // We will get a font substitution warning if we save a document with a missing font.
    doc.FontSettings = fontSettings;
    doc.Save(ArtifactsDir + "FontSettings.EnableFontSubstitution.pdf");

    using (IEnumerator<WarningInfo> warnings = substitutionWarningHandler.FontWarnings.GetEnumerator())
        while (warnings.MoveNext())

    // We can also verify warnings in the collection and clear them.
    Assert.AreEqual(WarningSource.Layout, substitutionWarningHandler.FontWarnings[0].Source);
        "Font '28 Days Later' has not been found. Using 'Calibri' font instead. Reason: alternative name from document.",


    Assert.AreEqual(0, substitutionWarningHandler.FontWarnings.Count);

public class HandleDocumentSubstitutionWarnings : IWarningCallback
    /// <summary>
    /// Called every time a warning occurs during loading/saving.
    /// </summary>
    public void Warning(WarningInfo info)
        if (info.WarningType == WarningType.FontSubstitution)

    public WarningInfoCollection FontWarnings = new WarningInfoCollection();

See Also