How do I open a file that was fine when I closed it, but now has warnings and will not open?

I have a couple of files in Microsoft Works Word Processor that I have opened many times with no problem. Now the following prompts pop up and I cannot get either file to open :

In order to open this file, Works needs to use a file converter, which may pose a security risk if the file you are opening is a malicious file. Choose OK to open this file if you are sure it is from a trusted source.

I choose OK and this warning pops up:

Works cannot open “C:\Users\....\Documents\....\....wps”. The file may be in use by another application, the file format may not be supported by any of the installed converters, or the file may be corrupt.

Then it closes out.

Notepad and Word will open them, but they are incomplete and have a lot of extra junk (alien symbols and letters). I created the files so they were not imported nor did they come from an outside source. The only thing I can think of that I did different before closing one of them was to change the font size.
Ideas, suggestions?