"This is not a valid Portable Document File (PDF)..." random error in Photoshop

As other's have said it's a clipboard issue.

For me it only happens when I use Teamviewer (same thing can happen with Parallels), which has a 'Use Shared Clipboard' function to copy something from a remote machine. This functionality will also corrupt the clipboard if pasting between illustrator and other adobe apps (including another illustrator document). And this corruption is what photoshop is complaining about. If I turn off 'use shared clipboard' in teamviewer then everything is as normal.
This might help someone, so I'll add it to this thread.

Same here, Macbook Pro.

Also getting this box. Any luck figuring it out?

Happened to me AGAIN today.  Clipboard was empty so that's not the issue.  I'm running the latest Mac OS Ventura 13.0.1 and the latest Adobe Creative Suite Apps.

Crazy how this is STILL an issue and there is not a fix for this four years after it first started happening to me.

Adding myself to this thread, also. This just started happening to me recently, so I was surpised to see this issue is at least three years old! Somewhat relieved to know it's likely not a virus. I was wondering if I needed to report it to the IT department...

Adding myself to this as I get the same error. It seems dodgy as it happens when I'm not using the app. Photoshop open in the background with no files open. What's it trying to do?

Macbook Pro 16 Intel 2019

macOS Monteray 12.6

Photoshop 24.0.0

Following up on a few things I've seen here as suggestions that might help but alas, I am still suffering from the dreaded "this is not a valid pdf" dialog box.  A few comments...

1. I've gotten the box twice over the last week - both times it was there when waking from sleep.  Each time, I did a paste afterward to see what was on my clipboard and it was always a string of text. So the theory of it being an image on the clipboard isn't true in my case.
2. Someone mentioned purging the clipboard would help but that doesn't seem probable as the clipboard is fluid and even when you purge it, the next time you copy something, the clipboard will have contents again.
3. I've trashed multiple versions of the preferences files to no avail.
4. Another mentioned disabling Optimize Mac Storage in icloud drive.  Mine is and always has been unchecked.  
5. I've turned off all the cloud (both Adobe Cloud (which I don't use at all) and Apple iCloud) connections within photoshop - everything saves/uses my local hard drive.

Those are all the things I've tried and nothing seems to have solved the problem.  It's not a work stoppage problem but it sure is annoying especially since it's a problem I can't solve!

Anyone else have any more things to try?

I stopped experiencing this error when I disabled the "Optimise Mac Storage" feature of iCloud Drive.

There are a few reasons why this might be the culprit:

• Adobe software doesn't support this feature (InDesign users are frequently pained by needing to manually re-download broken links in the Finder.)
• The error occurs after a period of time, e.g. After sleep or time away from Photoshop etc. This is typically when the optimise feature will round up large files and move them to the cloud. 
• The "PDF file" is possibly Photoshop's clipboard contents, which is stored in a location that gets optimised (the users library).

Just had this issue myself. Same error when starting Photoshop 2021 about PDF file not being recognised and it even did it when creating a new document using File->New. I originally suspected a rogue plugin, reset my preferences and even reinstalled PS.

However, for me at least, it was indeed something on the clipboard.  I simply overwrote the clipboard contents by copying some plain text from Textedit and the error went away. 

Only seemed to be Photoshop this affects though. Before I reset the clipboard content I started up Illustrator to see if I got the same error and it worked fine.