You can save the link to text file in Access table. Clicking on link in according textbox in form linked to this table opens the text file in default program estimated in your Windows. You allow (for folder where text files are) reading rights for specific domain group only (and reading and writing rights for another domain group, when there is a need for this).

When user belongs to domain group with rights to read only, then clicking on link opens the text file e.g. in Notepad in Read only mode. (Of course the user can edit the file and then save it to another location, but there will be no way to overwrite the original file.)
When user belongs to domain group with full rights, then the user can edit and save the file.
When user doesn't belong to either of groups, an error message is displayed when user is trying to open the file.