TrID is a tiny console-based tool for identifying more than 7,000 file formats from their content alone.
The program could be handy if you've found a file that's lost its original extension, or maybe it has an extension you don't recognise and you'd like to know what it is, or where it's come from.
Please note: TrID relies on a set of file definitions which aren't included in the download. To make it work, you must download the archive file from here and unpack it to the TrID folder (triddefs.trd and trid.exe must be in the same folder).
Once that's done, run the program by pointing it at any file, like this:
TrID then displays as many matching formats as it recognises, with the percentage probability of them being accurate. Here's what we got for a Word DOCX document:
TrID/32 - File Identifier v2.24 - (C) 2003-16 By M.Pontello
Definitions found: 7681
Collecting data from file: file
85.4% (.DOCX) Word Microsoft Office Open XML Format document (23500/1/4)
14.5% (.ZIP) ZIP compressed archive (4000/1)
DOCX files host Word documents in a ZIP container, and TrID had correctly identified them both.