Hi dave61430.
Yeah, I imagine that a 350MB file is a bit awkward to email!
You've got me curious now though. If Scribus creates a 350MB PDF whereas PagePlus - with the same images and text, or similar of equivalent size - creates a PDF of 35MB then either PagePlus or Scribus is doing something the other one isn't, but there's no way for me to know which.
Without access to PagePlus I can't do my own experiments but I have the feeling that PagePlus is doing something to the images that Scribus isn't. Whether it's compressing them, or re-sizing them, or cropping them, or a combination, or something else, I have no idea.
There's a chance that PagePlus is actually making an "inferior" PDF compared to Scribus. Unfortunately I don't know of any free software that lets you examine the contents of a PDF down to things like individual image information, but that sort of thing would help to show what was going on.
As an experiment I've just created a PDF from the full plain text of "Frankenstein, or the Modern Prometheus" by Mary Wollstonecraft (Godwin) Shelley. And at 12pt Arial, with fixed line spacing, it takes up 135 pages. This is exported to a PDF that is only 3MB (give or take a K or two).
So, in this simple test, Scribus doesn't seem to produce text in a way that adds to an excessive PDF size so I'd guess that the different file sizes are down to the images and the different ways Scribus and PagePlus export them to PDF.
Have you looked at your images to see if they can be "downsized" in any way? Are they at a visible resolution that is higher then you need, for example? Or are you only showing small portions of large images that could be cropped? I realise you've got lots of images but there are many tools available that can batch-change images quite easily.
It's a curious situation for sure. But I'm sure there will be ways of getting a smaller file size. You just need to figure out what PagePlus is doing to make the file size so much smaller.