The frustrating aspect of learning photoshop is that when learning it you will realise that you can accomplish the same task several ways. The following tutorials cover some of the different ways that you can open up different files in photoshop.
Opening an image
Professional Development for Educators – Opening an image in Photoshop on Adobe TV
This brief tutorial shows you how to open an image in Photoshop. This activity comes from the Adobe Professional Development Workshop, “Explore Creativity in Today’s Classroom”.
Opening an image without Photoshop
Photoshop definitely got it right with the PSD file format. It saves the complete state of a still-being-edited image so that you can close down and resume work later. When working with images, you should always keep a PSD copy around in case you need to make tweaks to the image later on.
Opening a PDF in Photoshop
Opening a PDF in PhotoshopOpening and Editing PDF Files in Photoshop (Adobe Photoshop CS6)