Generate document pages preview

GroupDocs.Signature provides PreviewOptions class to specify different options to manage document pages preview generation process.

Here are the steps to generate document preview with GroupDocs.Signature:

  • Create new instance of Signature class and pass source document path as a constructor parameter.
  • Instantiate the PreviewOptions object with: 
    • delegate for each page stream creation (see event handler CreatePageStream); 
    • image preview format - PNG / JPG / BMP, 
    • page numbers to process;
    • custom size of preview images (if needed). 
  • Call GeneratePreviewmethod of Signature class instance and pass PreviewOptions to it.

CreatePageStream delegate implementation

GroupDocs.Signature expects CreatePageStream delegate to obtain each page stream for image preview generation process

private static Stream CreatePageStream(int pageNumber)
{
    string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
    var folder = Path.GetDirectoryName(imageFilePath);
    if(!Directory.Exists(folder))
    {
        Directory.CreateDirectory(folder);
    }
    return new System.IO.FileStream(imageFilePath, FileMode.Create);
}

ReleasePageStream delegate implementation

private static void ReleasePageStream(int pageNumber, Stream pageStream)
{
     pageStream.Dispose();
     string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
     Console.WriteLine("Image file {0} is ready for preview", imageFilePath);
}

Generate document preview from file on local disk

public static void GetPreview()
{
    using (Signature signature = new Signature("sample.pdf"))
    {
        // create preview options object
        PreviewOptions previewOption = new PreviewOptions(GeneratePreview.CreatePageStream)
        {
            PreviewFormat = PreviewOptions.PreviewFormats.JPEG,
        };
        // generate preview
        signature.GeneratePreview(previewOption);
    }
}
 
private static Stream CreatePageStream(int pageNumber)
{
    string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
    var folder = Path.GetDirectoryName(imageFilePath);
    if(!Directory.Exists(folder))
    {
        Directory.CreateDirectory(folder);
    }
    return new System.IO.FileStream(imageFilePath, FileMode.Create);
}

Generate document preview from stream with custom stream releasing delegate

public static void GetPreview()
{
  using (var stream = File.OpenRead("sample.pdf"))
  {
    using (Signature signature = new Signature("sample.pdf"))
    {
        // create preview options object
        PreviewOptions previewOption = new PreviewOptions(GeneratePreview.CreatePageStream)
        {
            PreviewFormat = PreviewOptions.PreviewFormats.JPEG,
        };
        // generate preview
        signature.GeneratePreview(previewOption);
    }
  }
}
 
private static Stream CreatePageStream(int pageNumber)
{
    string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
    var folder = Path.GetDirectoryName(imageFilePath);
    if(!Directory.Exists(folder))
    {
        Directory.CreateDirectory(folder);
    }
    return new System.IO.FileStream(imageFilePath, FileMode.Create);
}

private static void ReleasePageStream(int pageNumber, Stream pageStream)
{
     pageStream.Dispose();
     string imageFilePath = Path.Combine("GeneratePreviewFolder", "image-" + pageNumber.ToString() + ".jpg");
     Console.WriteLine("Image file {0} is ready for preview", imageFilePath);
}

More resources 

Advanced Usage Topics 

To learn more about document eSign features, please refer to the advanced usage section.

GitHub Examples  

You may easily run the code above and see the feature in action in our GitHub examples:

Free Online App  

Along with full-featured .NET library we provide simple, but powerful free Apps.
You are welcome to eSign PDF, Word, Excel, PowerPoint documents with free to use online GroupDocs Signature App.

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