Viewer works locally, but not in Azure App Service

I am having a problem. I’ve tried everything I can think of, but I can’t get it to run in our Azure app service.

I’m using the code sample for the MVC Web Farm scenario.

In Azure, the file access is limited, but there is a %HOME%\site folder you can use to store files (see Operating system functionality - Azure App Service | Microsoft Learn). This maps to C:\home\site, so I’m using C:\home\site\doconut as my DoconutPngExportPath.

When I run it locally, it works perfectly, but when I run it in Azure, the Controller GET handler runs completely, but when the page loads I get an alert:

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Followed by

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And then it redirects to DocImage.axd with a “Missing document instance” message

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I’ve added logging code that indicates the ExportDocumentToPng is creating the files. I’m just not sure why it’s not able to read those files afterwards.

I’ve attached the relevant files: (3.1 KB)


Could you please send a complete example project without personal information so I can evaluate the problem?

This way I can better help you identify the issue that is occurring.
Thanks for your help.

Sorry, I’m just now getting back to this issue. I don’t have a complete example project, but additional info:

I’ve updated our application to mount an Azure storage account and I’m using that as the DoconutPngExportPath.

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Looking at the storage after loading the document viewer view, I can see it generated files in the appropriate place.

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I’ve downloaded these files and they all look OK.

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In the actual viewer, though, I’m mostly getting “Missing document instance.”

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If I look at the , I see DocImage.axd handlers. If I load this in a new tab and just refresh the page, it sometimes loads the appropriate file and sometimes loads “Missing document instance” for the same URL.

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Can you please download the latest sample package from the website?

In the following path you can find a sample using Azure:

Samples\NET Core\Cloud\Core.Cloud.Azure

Let me know if you have other questions.

We are using .NET Framework 4.8 and that sample is .NET Core.

It looks like it uses DocumentViewer’s ExportToCloud - which I assume will store the temp files in Azure blob storage. That would be great so we wouldn’t need to mount the storage as a drive.

Is there a .NET Framework equivalent to the DocImage.axd handling in Startup.cs? It looks like the DocImage.axd handler would need to know to read from blob storage. Or is there a way to configure the handler?


There is a sample in the Doconut ZIP for Webforms but it is very outdated.

This is the path of the sample:
\Samples\NET Framework 4.7\Cloud\WebForms.Cloud

Take a look in the web.config file in:


You need to config the node with the attribute name "DocImage".

In the comments on the web.config, you can see how to configure Azure with AzureStorageImageHandler.