Documents in Preview

Put all of the pages into the sidebar on the right. Drag them into the order you want. Select all the pages, File -> Print -> Save as PDF.

wdeponte wrote:

How can I group a multiple page, scanned document in preview and SAVE IT as 1 document?

It depends on the format in which each scan was saved. If it was PDF, then

Mac OS X v10.6: How to combine PDF documents using Preview

<http://support.apple.com/kb/HT4075>

If it was TIFF or JPEG, then, to my knowledge, you can't. You'll have to use something else.