This file is part and required by GDFImage GUI program, which allow you to build or extract you xBox iso files.
If you want to back up your original game disc, you can try Qwix or Craxtion. Qwix is a xBox and ISO management tool, with it’s transfer function, you can easily upload ISO files from computer to you xBox.
gdfimage.exe is not necessary for xISO, connect directly with a corssover, it’s easy and fast. You can extract files to xBox with ftp or CloneXB, which allow you to xBox DVDs to a GDF ISO image. The first time you start up the xbox with cromwell, it will ask for a new bios disc, you need to install the bios disc.