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Slow conversion of certain PDF to HTML in .NET


A customer reported rather slow conversion with certain PDF files (one sample file attached).
Rechnungen_0718_0004_0001.zip (425.6 KB)
On my machine it took about 10-12 seconds with GroupDocs.Viewer 22.5.
It’s a single page PDF with a size of 430 KB.
If I convert a similar filet (single page PDF with 464 KB), the conversion is done in 2-3 seconds:
docket test gp.zip (432.7 KB)

I tried to change image quality options, but that did not have a significant effect.
Can you please check what makes this certain PDF conversion so slow?

using (var viewer = new Viewer(documentPath))
	var infoOpts = ViewInfoOptions.ForHtmlView();
	var info = viewer.GetViewInfo(infoOpts);

	var options = HtmlViewOptions.ForEmbeddedResources("output_viewer{0}.html");
	options.SpreadsheetOptions = SpreadsheetOptions.ForOnePagePerSheet();
	options.SpreadsheetOptions.RenderGridLines = true;
	options.SpreadsheetOptions.RenderHeadings = true;
	options.RenderComments = true;


We’ve reproduced this issue, the issue ID for reference is VIEWERNET-3999. We’ll let you know when we have any information.

1 Like


GroupDocs.Viewer for .NET 23.8 includes performance optimizations that improve rendering speed and memory allocations. The package is available at:

Have a nice day!