It is possible to open a read-only or locked data file by checking the "Allow Read Only Data file Use" option in the database preferences under the Database Management-> General Settings theme.

In some cases like when stored on a non-rewritable volume type such as CD-ROM, a read-only data file needs to be opened and this setting will apply. By default, this option is not checked, which forces 4D to display a warning message when trying to open the locked data file and prevents from opening it. This prevents inadvertent use of a locked data file which modifications would not be saved.