Documents in Libraries Now Show Only Open with Windows Photo Viewer

All of the documents, regardless of how they were created and saved (word, pdf, etc.) now have an icon showing they open with Windows Photo Viewer. However, when I click on document to open it, there is this message "Windows Photo Viewer can't open this picture because either Photo Viewer doesn't support this file format, or you don't have the latest updates of Viewer." I don't want them to open in Photo Viewer. I want them to open in their original file extension -- Word, Adobe, etc. This happened when I selected one pdf document (in a folder with many files with differing file extensions) and selected export to jpeg. I've done this in the past with individual files with no problem. This time, it has applied it to EVERY file in all of my documents (including dropbox) files on my desktop. How do I get the files back to opening with their original file extensions?

Thanks, Brink. I think that may have taken care of the problem. At least the files look "right" now and they seem to be opening in the right format. I do appreciate your help!