You don't need to change that... Just set pages per sheet to 2 it the Print menu - and there you go!
Thanks! But.. heh. how exactely I do that? My Adobe Reader is in portuguese and the "set pages per sheet" may become very general when translating. Do I do this after clicking in the print button, and there I make these settings?
The point is that I don't have a printer set at the moment, but I'd like to make this conversion on the document just to view it.
If you use Adobe Reader 7, when you open the document look in the bottom right corner. There should be two square boxes next to each other. (Excuse the bad graphics):
Currently, it might be set at 
Click on the icon that looks like  
This will work for viewing, but not printing, and it will not save the changes to the document unless you have the full version of Adobe Acrobat.
Hope this helps!
So, when you open the Print dialog from the File menu, the first line says the type of your printer, or the printer attached to the computer you want to print it on. There must be a Properties button around this line. If you click on that, an other dialog pops up, where you can adjust paper size, resolution, and some other things. There must be a spinbox also (a box with a number in it and up / down arrows on the right side) saying x pages per sheet. If you're lucky, and the printer you intend to use is a state-of-the-art model, you may even find a Booklet printing option. That means that it will be printed in such a way that you can staple it in the middle and you get a real booklet. (First printed page, side 1: last page, first page, side 2: second page, last-1 page, and so on.)
If you do want to create a PDF file like that, instead of print it in the way you like, here are two packages that you should think.
It is able to print up to 4 pages in one page
It creates a virtual printer. Your output will be transformed into a PDF file in the format that you want.
Wow, that helped me too..Thanks a lot. I think fineprint is really good.
hmm.. where do I get a non-trial version? Btw... are they shareware as I'm thinking they r?
I use PDF converter to JPEG.
and print in with ACDSee 2 picture in one page .
If want to save i use macromedia flash paper to get Paper from printing and save to pdf .