This very issue I ran into as well for not so long ago yet it came in the slightly different way. Literally, I could save a project in pdf extension, the trick was it wasn't opening or doing so as one blank page. What helped me, I uploaded that corrupted document to the editor, exactly this one
https://ds11.pdffiller.com yet you might well use Acrobat or Foxit or whatever you have. I just opened it there and saved as a new file - and everything has been fixed