You easily can transfer photos from Picasa to Phototheca. Basically, to get your photos from Picasa to Phototheca you don’t need to do anything special. Just run Phototheca, go to menu item File->Import to Library, then browse to the folder with your photos, select one or many folders and press the Import button – that’s it.
Phototheca starts the importing process and after a while, all your photos appear in Phototheca. You’ll be able to keep all photos in Picasa while trying Phototheca, it does not move photos away from Picasa.
Read more: Overview of importing