When you save, use "SAVE AS" and when the window comes up, on the upper right
bar you'll see "Tools" - select that and then "properties." In the
properties window you may see the "Read Only" box checked. If so, uncheck
that, then click "Apply" then "Yes" to the popup about applying to sub
folders. Then Click on "Tools" again, and in the "Save Options," make sure
you select "Embed TrueType Fonts," otherwise if you attempt to edit the file
on another machine that may not have all the fonts you used, it will turn
itself into a read-only file.
Good luck!