When you save your work, save the files as Open Office files as well. . .
I use Open Office from time to time to convert MS Word documents to PDF's.
When you start Open Office Writer, you can open a document or file from another word processing program. When you finish working with that file, use the "Save as" command to save it as an "ODF text" file.
If you don't want to change the formatting of the original document, stop there. If you DO want to save the new changes in the original document, do another "Save as" and select the original document formatting.
Inversely, if you've created an Open Office document and want to convert it to a different word processing program, open the document, use the "Save as" command and save it as whatever type of program file you'd like.
I don't know about you but now I'M confused. Give it a try.
Hope that helps.