GEDITCOM  This comment is not true. GEDitCOM can open absolutely any GEDCOM file from any source. The only possible problem is if the source provides a bad GEDCOM file (but even then GEDitCOM can open it and tell you that it is bad by "checking the file for errors").

Perhaps this commentor is referring to a possibility that a foreign GEDCOM file is dimmed in the file opening dialog box. This dimming is done by MacOS and not by GEDitCOM. For this reason, there is a pop-up menu in the file-opening dialog box that can be used to select "All Documents" and then you may try to open any file. It is a standard Macintosh method for helping any application open files that may not be correctly identified by MacOS as belonging to that application.

If the commentor was looking for an "import" command, that is not needed since GEDCOM is the native format for GEDitCOM. One simply opens a file and does not need to import it.  
(Version 3.72)