Try an example
What are we looking for?
For a AI file, we look for the byte sequence %PDF which identifies that it is a PDF file, which Illustrator uses. Try changing the name of an AI file to a PDF, and see that it is the same.
Try your own
Or enter your own URL to analyse the first six sectors of the file:
File contents analysis
-- File contents go here. Click on a file from "Try and Example" to view.