Hmmm.
Unless you've chosen to save your documents in different formats, anything saved from Wordpad would normally be a Rich Text document (.rtf), anything saved in Microsoft Word 2007 onwards would normally use the .docx format and anything from an earlier version of Word would have a .doc file extension. So those are the file extensions I would expect to see associated with your documents.
I can't see how installing Windows 10 could possibly change your file extensions but it might well have accidentally changed your file
associations (i.e. the programs used, by default, to open each file type).
How are you trying to open your files? If it's by simply double-clicking on them I suggest forgetting that for the moment and opening the required program (such as Microsoft Word) FIRST and THEN going to File > Open to see if the documents will load normally. (If they'll load that way then you'll need to address the file associations problem later but there's no point worrying about that until you've tried opening the documents from within a program, rather than by double-clicking on them).
Also, in case it's Microsoft Word that's become corrupted, I'd try installing OpenOffice and then opening your files with OpenOffice Writer:
https://www.openoffice.org/
(If they're OK in OpenOffice Writer, but not in Microsoft Word, it will suggest that you need to reinstall Word).