I am a total newcomer to digital photograpy but I understand that jepg files will lose informationas they are manipulated in any way, even by simply opening and closing a file.
If you mean by opening and saving a file, Yes (if it's JPEG). The editor is going to recompress it when you do that (and if you have JPEG quality set lower in the editor, it can degrade it). If you open it and close it without saving, No (it won't degrade it).
Here is an article you may want to read written by Mike Chaney:
JPEG Images: Counting Your Losses