The first thing to do is to ensure your Office installation is working properly. To that end, try repairing it (via Windows Control Panel > Programs > Programs & Features > Microsoft Office (version) > Change > Repair).
Corrupt documents can often be 'repaired' by inserting a new, empty, paragraph at the very end, copying everything except that new paragraph to a new document based on the same template (headers & footers may need to be copied separately), closing the old document and saving the new one over it. With the problematic files you're receiving, it might be best to start off by doing this before making any other edits.
Similarly, corrupt tables (which the above process won't repair) can often be 'repaired' by:
• converting the tables to text and back again;
• cutting & pasting them to another document that you save the document in RTF format, which you then close then re-open before copying them back to the source document; or
• saving the document in RTF format, closing the document then re-opening it and re-saving in the doc(x) format.
Do note that some forms of table corruption can only be repaired by the first method.
Another fairly common source of problems is a cluttered temporary files folder. Orphaned .tmp files can accumulate over time as a result of crashes or shutting down the computer without first exiting all programs. See:
https://support.microsoft.com/en-us/...emporary-files. You might try closing all programs, then navigating to:
C:\Users\%Username%\AppData\Local\Temp
and deleting anything you find there. Windows might complain a few files are in use, but anything else can go.