It seems the only way to produce .pmg files from .pmd document would be to use the program from which both of these formats originate, Adobe Pagemaker. Since the program is discontinued you probably will have hard time finding it and perform this conversion however.
Convert Adobe PageMaker document to Adobe Pagemaker group file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert pmd to pmg on Windows
One of the first desktop publishing programs, introduced in 1985 by Aldus Corporation, initially for the then-new Apple Macintosh and in 1987 for PCs running the then-new Windows 1.0.
It was later bought by Adobe and rebranded Adobe PageMaker. The last version Adobe PageMaker 7 was released in 2001 and in 2004 the product was discontinued and slowly replaced by Adobe InDesign.
Convert from pmd file
to pmg file
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.