Keep workbook in read only state

Is it possible to give a client a workbook that will stay in read only state?

Example… I have a customer who purchases a full functional workbook and uses it for a year and creates a years worth of saved files. After the year I still want them to be able to open the saved files to view them, but not be able to use the workbooks functionality, make new files, make changes, etc. Is there a way to create a workbook under the same build key that will stay in read only when they open a saved file?

XLS Padlock doesn’t have this ability (yet, we added it to our TODO list).