Question How do you combine PDF files?

I scanned about 100 pages to PDF. I then scanned another 15 pages to a different PDF. Each page is an image. I'm trying to figure out how to combine both PDF files in Adobe Reader X.

 

Thanks, I'll check it out tomorrow.

 

I downloaded both the editing and merging apps. Both work like a champ. Only thing about saving an edited file is that it puts a watermark on it because I'm using the free app instead of the for pay Pro. Not an issue for me.