Sick of Watermark
You cannot import one project (project.prel file) into another project (project.prel file).
There are two approaches to using the content of one project in the another project.
a. Copy/Paste Insert. This uses Premiere Elements in conjunction with the ClipMate program.
b. Exporting the content of the first project to a file format consistent with the project settings of the
second project, and then importing that file as source media into the second project.
More details will be furnished with more information from you, starting with
What version of Premiere Elements are you using?
On what computer operating system is your Premiere Elements running?
What are the properties of the media involved? What are the involved project settings?/
Looking forward to your follow up.