How to Convert PDF to Fully Black & White (Grayscale) Using Aspose.PDF 21.6.0 (.NET Core 3.1)

Aspose.PDF Product Family
1

Hi Team,

We are using Aspose.PDF for .NET (version 21.6.0) on .NET Core 3.1, and we need to convert PDFs to fully black & white (grayscale) when a flag is enabled.

Our requirement:
:arrow_right: The final output PDF must be completely grayscale — no color in any images, shapes, vectors, or text.

We are currently using RgbToDeviceGrayConversionStrategy, but we are seeing that some PDFs still contain colored elements after conversion. This happens especially with images, vector graphics, and certain complex content.

Code We Are Using Now

private void ConvertToPdf(string inputFilePath, string outputFilePath, bool blackAndWhite)
{
    try
    {
        using (var pdfDocument = new Document(inputFilePath))
        {
            if (blackAndWhite)
            {
                Logger.InfoFormat("PDF to PDF- Applying black and white conversion");
                ApplyGrayscaleConversion(pdfDocument);
            }

            PdfFormatConversionOptions options = new PdfFormatConversionOptions(PdfFormat.PDF_A_3A);
            pdfDocument.Convert(options);

            Logger.InfoFormat("PDF to PDF- File saving process started");
            pdfDocument.Save(outputFilePath);
            Logger.InfoFormat("PDF to PDF- File saving process finished");
        }
    }
    catch (Exception ex)
    {
        Logger.ErrorFormat(ex, "Conversion failed for {0}. Error:{1}", inputFilePath, ex.Message);
        throw;
    }
}

private void ApplyGrayscaleConversion(Document pdfDocument)
{
    var strategy = new RgbToDeviceGrayConversionStrategy();

    for (int i = 1; i <= pdfDocument.Pages.Count; i++)
    {
        try
        {
            strategy.Convert(pdfDocument.Pages[i]);

            if (pdfDocument.Pages.Count > 100 && i % 50 == 0)
            {
                System.Threading.Thread.Sleep(10);
            }
        }
        catch (Exception ex)
        {
            Logger.ErrorFormat(ex, "Page {0} grayscale conversion failed. Error{1}", i, ex.Message);
        }
    }
}

Question

What is the correct or recommended way in Aspose.PDF (21.6.0) to ensure that the entire PDF, including images and vector elements, is fully converted to black & white?

We are looking for the proper API or official approach that guarantees that no color remains in the final output.

2

@ragu2736

Based on limited evidence (treat as hypothesis), here is a cautious take:
Summary of what is happening:

  • I could not confirm a documented solution for this scenario yet.

Why it matters:

  • Nothing in the current knowledge base matches this scenario, so proposing specific settings would be guesswork.
  • To avoid misleading guidance, I prefer to pause instead of speculating.

Next steps: please share a minimal repro (HTML/PDF snippet, SDK and version). I’ll check against the latest docs and release notes.

Assumptions / confirmations needed: SDK + version, file types, minimal sample, and exact error/output.

4

@ragu2736
Could you provide example of document where RgbToDeviceGrayConversionStrategy is not working to make document completely black & white?