I think both can be a problem.
It is relatively easy to test: save your project under a new name and in that new file delete all DWGs and see if the speed improves. If it does then the DWGs are the reason.
Or delete all the PDFs and see if the speed improves. If it does then the DWGs are the reason.
If you delete all DWGs and PDFs (placed bitmap image files may also be a source of slowness) and the file is still slow, then probably the size of the model is the cause.
Laszlo Nagy, Moderator, Site Admin https://twitter.com/laszlonagy AMD Ryzen 1700X 3.4 GHz, 32 GB DDR4 RAM NVidia GTX 1060 6GB, 500 GB NVMe SSD 2x28" (2560x1440), WIN10 PRO ENG AC18-AC21 Loving ARCHICAD since 1995