Watch Out When Formatting Starts to "Slip"
The Problem:
The formatting in my documents sometimes "slips"for example, I applied boldface to some text, but it changed back to the regular font after I edited another section of the document and then returned to it.
The Solution:
This isn't a fix, but an emergency warning. Formatting slipping like this means that the document is getting corrupted. Save the contents of your document in another format before the corruption gets worse. Choose File 
Save As, select Rich Text Format in the "Save as type" drop-down list, and save the document as a rich text file. Close the document, and copy the rich text document to a backup medium. Then create a new Word document, choose Insert File, insert the contents of the rich text file, and save the document. Check the document all the way through for missing text.