Some authors (for example, of forms to be filled out) “lock” their documents under Windows. This is annoying, as it prevents you from fixing errors or adding anything to the document.
If you web-search on “unlock word document” or “unlocking word document” you get a bunch of pages with advice that doesn’t work under Windows, or pointers to paid software. Here is a method that works, and is free:
1. Open your document in Word, then save it in “.xml” format.
2. Open the .xml doc in wordpad, notepad, emacs, or your favorite text editor.
3. Search for the string w:enforcement=”1″.
4. Replace the “1” with a “0” to disable enforcement (this step unlocks the document).
5. Save the .xml document from your text editor.
6. Open the .xml document in Word.
7. Choose “Save as…” and save it as a .doc or .docx file.
Your original Word document can now be edited normally. Enjoy!
SOURCE: http://people.csail.mit.edu/seth/misc/unlockworddoc.html