Read Only Warning

There is a way to do this, but it would involve putting VB code into every file and it would only work for XLSB and XLSM files. This doesn't sound practical.

Another method is to give the user an "executive" excel spreadsheet with a file chooser and when they select a file, the executive program checks the file properties and either puts the remark in a cell as you suggested or pops up another warning if the chosen file is read-only. The issue here is getting the people to use the executive spreadsheet instead of regular excel or even the windows explorer to get to the file.

There is nothing native in the settings in Excel or Windows that I know of that allows a change to the way read-only files are opened.

The file name at the top should show that the file is READ ONLY as well - not that this helps much. However, if they lose all their data enough ti,es, it will eventually sink in. You cannot cover every thing users might try