Error message with PDF, editing?

I would like to write in a PDF document, but it always shows me "the input value is invalid". This is only the case for certain places (when I enter numbers). Can someone help me there? Unfortunately I can't find any useful articles in German on the Internet, my English is not really pronounced.

I use: HP laptop with Windows 10 (latest version)

Browser: Google Chrome and Microsoft Edge (their PDF viewers always show me this error message).

So I would use https://pdf2docx.com/de/. Simply insert the PDF and you have a Word document where you can make your changes. Then you can export it again as a PDF via Word.

I recommend this tool: https://www.getfreepdf.de/ It can be used to create and edit PDFs. The operation is like a layout program.