How to Know a PDF is Corrupt
Open a PDF in Adobe Acrobat DC. Then without doing anything else, close the PDF. Does Acrobat ask to save changes even though you made no changes? If so, then it means that Acrobat auto-fixed a corrupt PDF.
Open a PDF in Adobe Acrobat DC. Then without doing anything else, close the PDF. Does Acrobat ask to save changes even though you made no changes? If so, then it means that Acrobat auto-fixed a corrupt PDF.