Jan Kučera

If the reason is that the application is unresponsive, I guess OS can decide how it wants to indicate this to user (such as washed out UI). Or is the...

Would you be able to provide a repro project?

There is https://github.com/dotnet/wpf/blob/0310ea93a4ea4af6123dc5de3da1e3e3ee582100/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Data/ListCollectionView.cs#L2585-L2613 but without repro it would be difficult to check whether that is the cause of the issue

Thank you! It does appear indeed that moving the lines 2610-2613 after 2585 mitigates the issue.

If you are on .NET Framework then I am afraid this won't get fixed, you would have to file a business case.

You could just try to open non-PDF file to test this :) Hm, none of those options are available to me: But also I can see in your screenshot that...

The v3.1.2 is happy with letting me open the same file on the same machine in Adobe Reader: The files I have to open are encrypted and protected by the...

I think your test file is good enough to make it to `WndProcCanvasLoadError`, which is not my case. My case seems to behave the same way as when you try...

Yes, and my point is that files which are "PDFs not recognisable as such" opened in tabs/windows of SumatraPDF before and it allowed them to be reopened in Adobe Reader,...

As far as I can tell it is actually a valid PDF using Security Handler specified in the Filter entry as per the PDF specification. Adobe Acrobat checks online what...