I didn't know where to put this information. Maybe it is of interest for someone.
PDF Validation with ExifTool – quick and not so dirty
https://openpreservation.org/blogs/pdf-validation-with-exiftool-quick-and-not-so-dirty/
Interesting, but I don't know how they get ExifTool to run so slowly. They say it takes 1 minute for a 1 MB PDF file, but on my system it takes 0.17 seconds to run exiftool -validate on a 10 MB PDF.
- Phil
Edit: OK. It turns out this was the time for 1000 files, not 1.
Since I also don't know how it is implemented there, it could possibly also be problem with "Common Mistakes when using ExifTool, 3. Over-scripting".
https://exiftool.org/mistakes.html#M3