I have several A4 PDF documents which I would like (two into one) \"glue\" together into A3 format PDF document. So I will get from 2PDFs A4 a single one si
I would combine the two A4 pages into one 2-page PDF using pdftk. Then Print to PDF using something like PrimoPDF, and tell it to print to A3 format, two pages per side.
I just tested this printing some slides from PowerPoint. It worked great. I selected A3 as my paper size in PowerPoint, and then chose to print 2 pages per side. Printed to Primo and voila, I have two A4 slides per A3.