PDF's no longer work after import into Calibre?

Cyber-Wizard · Today, 06:59 AM

Calibre Version: 8.15
OS: Windows 11 Pro 25H2

Recently I've noticed that, after I import some PDF's into Calibre, the PDF can no longer be opened.
I don't generally test books after importing them into Calibre as I understood that Calibre doesn't do anything to PDF's on adding them, they just get copied into a library folder.

Over the last week I have opened up three PDF's after adding them to Calibre and upon opening them I get an error stating that the PDF document is invalid.
I have been using PDF Studio Viewer for some time now and I tried switching my default viewer to Chrome but still get an error.

I can open up the original PDF in both applications without any issues.
If I try to open up the PDF directly from the folder where Calibre stores it after adding I still get an error.
If feels not so much as something that Calibre does when allowing the document to open in my default PDF viewer as it's something that has happened to the PDF when Calibre copies it to the library folder.

I don't usually open them after adding so I'm not certain how long this has been happening.
It also doesn't happen with every PDF. Out of 5 that I added today, only two failed to open after they were added to Calibre.

Has anyone encountered this and perhaps found a fix?

Quoth · Today, 07:13 AM

Where is your Calibre Library stored?
Make sure AV and OneDrive are excluded.

kovidgoyal · Today, 07:43 AM

unless you have some third party plugins like the nodrm plugin installed importing a file into calibre leaves it byte-for-byte identical.

Cyber-Wizard · Today, 08:54 AM

Quote:

Originally Posted by Quoth

Where is your Calibre Library stored?
Make sure AV and OneDrive are excluded.

The library is local to the machine in my Documents Windows library.

OneDrive isn't in use.
I'm using Windows Defender. I would expect it to have less of an impact than a 3rd party AV. I can check that.

Cyber-Wizard · Today, 08:59 AM

Quote:

Originally Posted by kovidgoyal

unless you have some third party plugins like the nodrm plugin installed importing a file into calibre leaves it byte-for-byte identical.

I've been scrolling through my previously added PDF files and can't seem to find any others that won't open.

Since this isn't happening with all PDF's, only some, testing older ones isn't in any way evidence that the problem started recently. The last batch of PDF's I imported was in Sept/Oct and I can't find any of those that won't open. It's only been occurring with any I've added in the last couple of weeks.
It's really odd.

The only plugins I have installed are Goodreads, Find Duplicates, and Kobo Utilities.

kovidgoyal · Today, 09:06 AM

Since you say you have the non-imported originals still, try re-importing it and see if the file changes.

Cyber-Wizard · Today, 09:07 AM

I just found that if I add one of the PDF's that doesn't open into Calibre a second time then it works just fine.

I don't appear to be low on CPU or memory resources. At the moment I do have a folder scan running on a NAS folder in ComicRack that could explain the ones that were imported earlier today and wouldn't open.
I did find this same issue last week when I didn't have any other apps open but it seems very likely that something has "interfered" with the PDF as Calibre makes it's copy.

Today, 06:59 AM	#1
Cyber-Wizard Junior Member Posts: 4 Karma: 10 Join Date: Nov 2025 Device: Rakuten Kobo Aura	PDF's no longer work after import into Calibre? Calibre Version: 8.15 OS: Windows 11 Pro 25H2 Recently I've noticed that, after I import some PDF's into Calibre, the PDF can no longer be opened. I don't generally test books after importing them into Calibre as I understood that Calibre doesn't do anything to PDF's on adding them, they just get copied into a library folder. Over the last week I have opened up three PDF's after adding them to Calibre and upon opening them I get an error stating that the PDF document is invalid. I have been using PDF Studio Viewer for some time now and I tried switching my default viewer to Chrome but still get an error. I can open up the original PDF in both applications without any issues. If I try to open up the PDF directly from the folder where Calibre stores it after adding I still get an error. If feels not so much as something that Calibre does when allowing the document to open in my default PDF viewer as it's something that has happened to the PDF when Calibre copies it to the library folder. I don't usually open them after adding so I'm not certain how long this has been happening. It also doesn't happen with every PDF. Out of 5 that I added today, only two failed to open after they were added to Calibre. Has anyone encountered this and perhaps found a fix?

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Today, 07:13 AM	#2
Quoth Still reading Posts: 15,173 Karma: 111120239 Join Date: Jun 2017 Location: Ireland Device: All 4 Kinds: epub eink, Kindle, android eink, NxtPaper	Where is your Calibre Library stored? Make sure AV and OneDrive are excluded.

Today, 07:43 AM	#3
kovidgoyal creator of calibre Posts: 45,664 Karma: 28549046 Join Date: Oct 2006 Location: Mumbai, India Device: Various	unless you have some third party plugins like the nodrm plugin installed importing a file into calibre leaves it byte-for-byte identical.

Today, 09:06 AM	#6
kovidgoyal creator of calibre Posts: 45,664 Karma: 28549046 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Since you say you have the non-imported originals still, try re-importing it and see if the file changes.

Today, 09:07 AM	#7
Cyber-Wizard Junior Member Posts: 4 Karma: 10 Join Date: Nov 2025 Device: Rakuten Kobo Aura	I just found that if I add one of the PDF's that doesn't open into Calibre a second time then it works just fine. I don't appear to be low on CPU or memory resources. At the moment I do have a folder scan running on a NAS folder in ComicRack that could explain the ones that were imported earlier today and wouldn't open. I did find this same issue last week when I didn't have any other apps open but it seems very likely that something has "interfered" with the PDF as Calibre makes it's copy.

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