Importing Photoshop patterns is super easy. This is for the more recent versions, go to the window menu and select patterns to display the panel
Go to the right side menu and click and then import command. Browse for PAT files. Select one or more PAT files
You will see all the tiles added in groups with the same names as the original files.
Select one of the presets from the panel and drag to the art board and add a fill layer in seconds
Before, the most recent versions, you would have had to either add the PAT files along side the PAT files added by Adobe into the presets section and load / replace them via a variety of panels. You could also browse for those files via the load command / replace command.
Once you have pulled into your favourite application more and more presets for use with your brushes (via the textures feature) as well as fills and fill layers and also as overlays in layer effects and more, you can create even more amazing work. They can be used as overlays, backgrounds. brush strokes, textures and more