A well-formed GEDCOM follows the GEDCOM standard. Various versions of the standard exist. Most software products DO NOT follow completely any of these versions or have created their own "extensions" to the standard. So you will need to know what those products support and what FTM20XX produces and/or supports.
You must experiment, most of these products say they support GEDCOM and most don't have a clue.
Look here for more information and check out the "External links" for links to copies of the different versions of the standard, however the article is not 100% correct in it's use of terminology regarding the word "Standard": http://en.wikipedia.org/wiki/GEDCOM
That being said: Most people don't care about GEDCOM because once they start using one program they either stay with it forever or live with the loss of data when sharing information. I only bring it up because I use GEDCOM a lot and have written utilities that read/write GEDCOM for my own data mining and reporting programs.