OK. I have part of this worked out .. the other part is still a mystery.
The part I worked out ..
There is a "Global" setting in Pagemaker to embed files.
Go to
Utilities > Plugins > Global Link Options This window allows you to set text and images to be embedded on import.
This is what is causing the document to grow. NB. The 1GB file had 000's of images that were not linked. Linking the images caused the file to continue to grow. When the linking was finished the file was 1.4GB.
Maybe Pagemaker or the workstation needed a reboot??
The part that's unsolved ..
I have tried resaving the 1GB file that was submitted after changing this Global setting but it is still just as large.