I am sure that the problem is the size of the graphics, because 50MB is huge. The way I keep graphics under control is to edit them in another package and save them the final size and resolution needed in the document (and I usually use highest quality jpeg). If the document is only going to be viewed and not printed, then the quality can really be quite low before it is noticable (screen resolution is never more than 96dpi); even a tiny PNG is acceptable.
Once you have the graphics saved in the correct size and resolution for your document, use Insert, Picture from File to place them in the document.
I do this for any graphics, whether it is a digital photo, a graph from Excel or a complex network diagram created in Visio.
If you don't already have a suitable graphics editor, I highly recommend the free to download IrfanView which handles just about any graphics format and does everything you need for this task.
Regards: tf1