edit gnucash file in ubuntu

[Harold]

I have been using GnuCash in Ubuntu for a few years now. While trying to use GnuCash in Windows XP I posted to the group and was told to edit the backup file that I was using in GnuCash for Windows. So that got me to thinking about editing the file in Ubuntu. After using the archive manager to open the Ubuntu file I get an error when trying to extract the file. I tried gedit and libre writer. Both game me an error. I thought the file to be extracted was a text file. What am I missing here?

Thanks,
Harold