I would use Acrobat Pro to combine PDF's it is the best way and the easiest but if you don't have it on your h/disc then use PS. From the file menu File > Automate > PDF Presentation,
1. Select the files you want to convert to pdf.
2. Select Multi-Page Document.
3. Click Save button.
..and then the Save abobe PDF window comes up, where you can define the pdf settings and then save it. Don't click on the "Presentation" save as "Multi-Page PDF Document"

Hope that helps. Hope that you didn't think in my first reply I was teaching you "to suck eggs" but as mod I have to cover all bases.