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 sided PDF A3. I have found the excellent utility PDFToolkit and some others but none of them can be used to "glue" side by side two documents.
Found the following (free and open-source) tool for doing Imposition called Impose (thanks danio for the tip). This solved my problem perfectly.
EDIT: Here is how it's done:
Use PDF Toolkit to joint two PDF files into one (two A4)
pdftk File1.pdf File2.pdf cat output OutputFile.pdf
Create from this a single page (one A3):
java -cp Multivalent.jar tool.pdf.Impose -dim 2x1 -verbose -paper-size "42.2x29.9cm" -layout "1,2" OutputFile.pdf