Winhex

Hi there.

This is my first time working with a hex editor so yes i am a newbie on this.

I am trying to use winhex to edit a cd image (iso) and remove the information about the path table but i can't seem to figure it out.

I am using the winhex trial version in "in-place mode" . When I use the "Replace Hex Values" with the option "Replace in Block only" selected, I get the following message:

Invalid file: user.txt. Do not proceed. and then I press o.k so many times and finally I get a message saying that "XX" was Replaced 0 times.

Could someone help me to figure this out please?

thanks in advance