PDF with metadataproblem & can't split

Hi!

I have a few pdf-books that won't show metadata correctly in my Kobos (Aura & Aura One). The author becomes "Unknown" and the title is the title of the file. It shows the book cover though.

And when I try to use an online pdfsplitter it says: "The uploaded file does not seem to be a valid PDF file".

I have no problem reading the files (whether on the computer or on my Kobos). And I have no problem adding metadata with Calibre.

Any ideas what can be wrong with the files?

Thanks!