When DROID starts up it attempts to load a local signature file. If none is found, it must download one. This is done automatically when the user gives their assent via a dialog box.
A new signature file can be downloaded from The National Archives' PRONOM website at any time:
The signature file is managed by The National Archives who will, from time to time, add new file formats and new binary signatures. It is therefore important to make sure on a regular basis that DROID is using the most up to date signature file. This can be done at any time by clicking on the Update Now button in the Options dialog.
DROID will prompt the user at startup to check for signature file updates if this has not been done for a configurable period of time. This time period can be configured in the Options dialog by changing the number of days to Check for update every ...