If you are migrating from CodeWarrior to KDS, then you might notice that CodeWarrior had a 'Add Files...' menu:
KDS is using an unmodified Eclipse version, and because the above menu was a CodeWarrior specific extension, this menu is not present in Eclipse.
But there are many different other ways in Eclipse how to add existing files to a project in KDS:
See How to Add Existing Files to Eclipse Projects | MCU on Eclipse
Happy Adding :-)