PDFtk is a tool for doing everyday things with PDF documents.

# To extract pages 1-3, 5 and 6-10 from a PDF file and save them as another one:
pdftk input.pdf cat 1-3 5 6-10 output output.pdf

# To merge (concatenate) a list of PDF files and save the result as another one:
pdftk file1.pdf file2.pdf ... cat output output.pdf

# To split each page of a PDF file into a separate file, with a given filename output pattern:
pdftk input.pdf burst output out_%d.pdf

# To rotate all pages by 180 degrees clockwise:
pdftk input.pdf cat 1-endsouth output output.pdf

# To rotate third page by 90 degrees clockwise and leave others unchanged:
pdftk input.pdf cat 1-2 3east 4-end output output.pdf