Follow the below steps to move Thunderbird files to PST file format. Download and install DRS Thunderbird Migration Tool. Run it as administrator. After that, choose the desired Thunderbird profile and press the Next button. Select the desired mailbox items from the preview and click Next. Expand the Save/Backup/Migrate As field and select PST file format. Now, choose the remaining migration options as per your need. At last, click on the Convert button to back up Thunderbird to PST.