for that purpose you can use the "Add password protection" in menu "File".

Here from the User Manual:

Saving Files as Run-Only

Isadora allows you to save your files as “run-only”, so that others can use the file but can only modify it specific ways. One place this might be useful is when Isadora is used to create installations that will be maintained by others. Making a document run-only means that only you will be able to modify the file.