Commands

Two PDF documents per Page (A5)

$ pdfjam --nup 2x1 file1.pdf file2.pdf --landscape --outfile DONESKI.pdf

# --nup 2x1   : side by side
# --landscape : Set page to landscape mode
# --outfile   : Set output file

Separate pdf documents

Source

$ pdfseparate [-f x -l y] input.pdf output-page%d.pdf

Join/concat pdf documents

Source

$ pdfunite input1.pdf input2.pdf output.pdf

or

pdfjoin input1.pdf input2.pdf

Join without rotation and addition of white space

Source

$ pdfjoin --paper a4paper --rotateoversize false ....

Create blank PDF from command line

Source

$ convert xc:none -page A4 blank.pdf