This may be a long shot, but try changing the suffix on the name of the document (make the change via the icon for the document). That is, if it is mydocument.txt, change it to mydocument.pages or mydocument.pdf; any word processing or text type of suffix (those just mentioned plus .rtf, .doc, .docx, etc.) other than the current one.
You will probably get a warning asking if you want to keep the original. Don't, but remember what it is so you can go back if you want to. Also, don't do something like mydocument.doc.pdf. Use only one suffix for this experiment.
