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Attempt to view .docx files produces an InvalidOperationException: "This is not a structured storage file"

The viewer.view produces an InvalidOperationException with the message This is not a structured storage file.

The document is fine (opens fine in Word) and my code works ok with PDF documents - no errors and the HTML and page counts etc are correct.

What is the error referring to and how can I fix this?


Thanks for contacting the support. It seems like it’s a bug, could you please provide the following information for further investigation:

  • API version that you’re using
  • Sample file


Sample file: (19.6 KB)




I’ve failed to reproduce the issue with (20.8 KB) the single page (42.4 KB) was rendered.

Please share more details:

  • Code snippet that you’re using or sample app
  • Your environment and target framework


Hi - as requested as snippet to demonstrate the fault. Is this correct?

The environment is Windows 10 and .NET Framework 4.8

var inputbytes = File.ReadAllBytes("file.docx");
MemoryStream mem = new MemoryStream(inputbytes);
string convertedHtml = string.Empty;
mem.Position = 0;
MemoryStream outputStream = new MemoryStream();
using (Viewer viewer = new Viewer(mem))
    HtmlViewOptions viewOptions = HtmlViewOptions.ForEmbeddedResources((pagenumber) => outputStream, (pagenumber, pagestream) =>
        pagestream.Seek(0, SeekOrigin.Begin); 
        using (StreamReader sr = new StreamReader(pagestream))
            convertedHtml = sr.ReadToEnd(); // get the stream data as an HTML string

    viewOptions.RenderToSinglePage = true;

    ViewInfoOptions viewInfoOptions = ViewInfoOptions.ForHtmlView();
    ViewInfo viewInfo = viewer.GetViewInfo(viewInfoOptions);




That’s right, thanks for the code snippet. Unfortunately, I can’t reproduce the issue on my local Windows 10 machine.

It looks like Viewer can’t detect filetype or detects filetype incorrectly because the memory stream is passed to the Viewer’s constructor.

Could you please try running the with (21.1 KB). in your environment and share exception details and log.txt file that will be created in the application directory?

One more thing, try passing LoadOptions as second parameter of Viewer constructor:

var filename = "resume_eight.docx";
var extension = Path.GetExtension(filename);
var filetype = FileType.FromExtension(extension);
LoadOptions loadOptions = new LoadOptions(filetype);

using (Viewer viewer = new Viewer(mem, loadOptions)) { ... }

While Viewer does support filetype detection this operation could be expensive so it is preferable to pass filetype when you know it.


Thanks Vladimir, that solves it when I pass the FileType in via the LoadOptions.

Thanks for your quick response.



You’re welcome!