You can try installing a PDF reader if none already installed (Adobe Acrobat is by far the most common, it's also very slow and bloated)
Otherwise you can try uninstalling/reinstalling your existing PDF reader
You can try installing a different PDF reader
https://www.google.ca/search?q=pdf+reader|viewerYou can try submitting your file to an online PDF reader (although I don't advise uploading any private/sensitive data to random websites)
https://www.google.ca/search?q=online+pdf+reader|viewerYou can try running a PDF repair tool (always on a copy of the unreadable file, not the original, in case it irreversibly changes/wrecks any data)
https://www.google.ca/search?q=pdf+repair
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