How do I save a SketchUp model as a PDF file?

Can I save a simple model as a PDF file and attach it to an e-mail?

It depends on what you mean.

SketchUp Pro has two methods (export a vector image directly, or put your view on a LayOut page and export that to PDF.
All SketchUp users can, of course, use a PDF printer (there are a zillion available from the costly Adobe Acrobat to many freeware and shareware ones) to print their view to PDF.

Then there is the 3D PDF that is a different beast altogether - it is a 3D model that can be viewed, zoomed and orbited in Adobe Reader, but you need a plugin to produce it. There are two available, from RPS Systems and SimLab, neither is free.