Hi ndhrgfrjkfk
Hopefully all the projects are the same dimensions. For
example, 640 x 480. Otherwise, you may see some unwanted or
unexpected results.
I'd probably take the following approach. Create a totally
fresh blank project sized appropriately. Then one by one, click
File > Import > Slides/Objects... and point at the other
projects.
Please do keep in mind that we normally recommend not
exceeding between 50-65 slides as a very general maximum. A lot of
the deciding factor is related to the overall project dimensions,
number of objects on each slide, how much audio there is, things
like that. You may get away with as many as 100 to 150. Certainly
I'd never want to exceed that.
Hopefully this helps... Rick