This option can be run at any time from the File Menu. It will check the integrity of the currently opened file, check for errors in the structure of the GEDCOM file, and optionally fixes any errors found. If you get unexpected errors, it's always worth running this option to check the file, especially if you have been editing the file with a text editor or with another program other than Family Historian.

You will be automatically prompted to Validate when opening any GEDCOM file that was not created by Family Historian.