Working with "invalid" PDF files on Acrobat online (web app broken)

I have a lot of PDFs that came from various places. Some of them appear to not strictly adhere to the letter of the standard... And acrobat online seems to not handle this at all. As an example, I have a file that I would like to add a comment ti, but the existing comments never load, and I get the visible message "Content is still loading. Please try again once loading is complete". Looking in the dev console I see the following:

{
"error": "corruptFile",
"errorCode": "std::invalid_argument,PDF date has malformed UTC offset."
}

So the "loading" never completes... Is there a way to fix this in Acrobat online, or do I need to run something over all my PDFs to be able to add highlights/comments them directly on the site?