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Why won't PDFs open reliably in Thunderbird?


I’ve installed Thunderbird on a client’s Windows 7 laptop and I’ve had
problems with PDF attachments not opening. Some do open; some don’t. When a PDF
file won’t open, a message pops up as follows, “There was an error opening this
document. The file is damaged and could not be repaired.” PDFs stored in the
document folder can be opened with no problems. I have upgraded Adobe to the
latest version; I’ve tried other PDF reader programs and I’ve made sure Windows
is up to date; I’ve done virus and malware scans and so forth. I’ve sent test
emails from a web-based account with a PDF attachment that opens okay with
Adobe but when I attempt to open the same PDF attachment within Thunderbird,
the error message pops up. Online research shows that others have had similar
problems dating back to 2005. I’ve tried all different solutions including
reinstalling Thunderbird; tried the latest as well as earlier versions. I’ve
done more research and there seems to be conflicting information on the reasons
and the solutions to the problem. I ended up uninstalling Thunderbird and
installing Incredimail so my client can open up PDFs without problems and it
looked more like Outlook Express which he used to use on this old computer. I
knew you used and recommend Thunderbird. Have you heard of this issue and what
is the fix for it?

In this excerpt from
Answercast #92
I look at some reasons why PDF files occasionally cannot be
opened from an email program.


Thunderbird PDFs don’t open

I hear about issues like this from time to time and it’s not always restricted to just Thunderbird.

What I believe is happening – and what is usually happening when I hear complaints of this particular kind of problem is that – it’s not related to Thunderbird; it’s not related to the PDF; it’s actually related to the anti-malware software that happens to be running on that computer.

Real-time scanning

What is probably enabled is called “real-time scanning of email” as it’s downloaded, or as it is opened by the user. That can cause interference.

It causes interference in a couple of different ways. The most common being that when you go to open the PDF, your anti-malware says, “Oh, I better scan that quickly before you open it.” But the PDF reader tries to open it a little too quickly – and the anti-malware software hasn’t let go.

So the PDF reader can’t open it. It knows the file is there but it can’t open it and one of the error messages that it may often throw in a case like that is that the file is corrupt.

Look at your anti-malware software

So my recommended, first step, solution to this is to examine the anti-malware software that’s running on that computer and see if there is an option to turn off, or disable, what I call “real-time email scanning.”

There may be other terms for it depending on what anti-malware solution you’re using – but the fundamental concept here is that it’s actually trying to scan email in more or less “real time.”

So that’s where I would point you first.

Time to load

My guess is that the reason it sometimes works and it sometimes doesn’t has to do with timing. Sometimes, perhaps, the PDF is small enough that the anti-malware tool can scan it quickly and release it in time for the PDF reader to open it up.

So, that’s where I would send you – your anti-malware software.

(Transcript lightly edited for readability.)

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3 comments on “Why won't PDFs open reliably in Thunderbird?”

  1. From past experience whenever I am unable to open an attached file in emails …. I save the file first then I open it and it always works.
    Try my trick….. you will like it.

  2. I was having a similar problem. I eventually solved it by selecting Tools > Options… > Attachments Tab.
    Scroll down to find “pdf file”, click in the Action column which gives a dropdown list. Select “Use Adobe Acrobat (in Thunderbird)” and Click OK

  3. I too have previously had an intermittent problem with pdfs downloaded into Thunderbird being corrupted. To try to pin down the problem, you should use the web interface to your mail server (easy when it’s gmail!!) and see if the pdf attachment is corrupted on the server. If not, then you know that it is (probably) Thunderbird related (as it was for me).

    The following link then suggests some parameter changes (fetch_by_chunks) in Thunderbird, and I haven’t had the problem since.

    Certainly worth a try.


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