Hi Joy,
There are some topics about GEDCOM in the Reference Library
http://surname.rootschat.com/lexicon/reflib-lexicon.php?letter=G&lang=EN&input_form=0but basically, it is a plain text file which is the standard interchange for various genealogy programs.
But ... and it is a big but ... some firms use a non-standard GEDCOM to enhance their own programs with stuff that isn't in standard, ... and to bind you to their product.
If you look at a GEDCOM file in an editor, you will see something like this:
0 HEAD
1 SOUR Legacy
2 VERS 7.5
2 NAME Legacy (R)
2 CORP Millennia Corp.
3 ADDR PO Box 9410
4 CONT Surprise, AZ 85374
1 DEST Gedcom55
1 DATE 22 Sep 2013
1 SUBM @S0@
1 FILE C:\Legacy\Data\ag-mm-02.ged
1 GEDC
2 VERS 5.5
2 FORM LINEAGE-LINKED
1 CHAR ANSI
0 @S0@ SUBM
1 NAME Not Given
0 @I9@ INDI
1 NAME Hanns /Margulies/
2 GIVN Hanns
2 SURN Margulies
1 SEX M
1 BIRT
2 DATE 27 Nov 1889
2 PLAC Sosnowice, (Russian-)Poland
1 DEAT
2 DATE 30 Mar 1960
2 PLAC London, England
1 _UID 37EE84C86B7142EEBBEF37DE17CA0B39619D
1 CHAN
2 DATE 9 Oct 2011
3 TIME 12:10
:
:
:
Note that most keys (in the 2nd. column) have 4 characters, and more important,
_UID has an underline.
The
underline is usually a sign that this is non-standard.
In this case it is an ID number that Legacy uses.
You could try making a copy of your GEDCOM file and then deleting all lines with a non-standard key and then see what it looks like in other programs.
BUT .... only do this with a COPY of the original GEDCOM file
Bob