Viewer can copy the file itself, but not the contents of the file.

If the file itself can be copied, then the contents of the file should also be copied. This is more intuitive and easier to understand.
Also, if the file itself can be copied, there is no security issue if the contents of the file can be copied.

The users just don't want the contents of the file to be edited.
Rather, they want the contents of the file to be copied.

The inability of viewers to copy the contents of files is ineffective in every respect.
Nonetheless, it just stresses the users out.

It should be improved.