I recently received an agreement in MS Word format which I wanted to fill out, but couldn't because it was protected/read-only. Opening the document in LibreOffice writer didn't significantly improve the situation.. whole sections of the document was still marked read-only.

Here's what I did to get around it:

1. Open .doc in LibreOffice Writer, save as .odt
2. Open .odt in AbiWord, make changes, save back to .odt
3. (optional) Open .odt in LibreOffice Writer and do whatever else you need to do

At this point, you're probably wondering: why not open the .doc in AbiWord in the first place? Well, AbiWord didn't import the .doc very well, with lots of formatting issues, missing characters etc. Using LibreOffice Writer to convert the .doc to .odt bypasses this.