How can I join two PDF pages

I have two portrait A4 PDF pages which I want to merge into one landscape A3 PDF page (i.e. put the two A4 pages side by side and get rid of any gap between them)…2 pages are now 1…

Does anyone know how to join PDF pages to make 2 pages into 1 in Adobe Acrobat 7?

Merge into two page document, then set paper size and 2->1 page compression in the print dialog.