pdf files won't open in preview

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Are these PDFs sent to you from Windows, Linux, or macOS? Find out how these PDFs are being created, and that may be a clue to what is corrupting them.

Can you right-click on the PDF attachment and save it to the filesystem, and then double-click it there and have it open in Preview?

In the Finder, single-click any PDF and press option+cmd+i to open a Get Info of it and see what the default opening application is assigned. Is it Preview, or something else?

You posted in the macOS Ventura community and when on Ventura 13.1 I can double-click a PDF attachment in Apple Mail and it immediately opens in Preview. I can also single-click that PDF and press the spacebar to open it in Quick Look.

There are some unusual PDFs that Preview cannot open or display correctly, but they are few and far between.