I had some schoolwork scanned to a PDF-document, with odd pages in one document and even pages in another. The pages was also in wrong order. I was looking for an easy way to rearrange the pages in a single document. No fancy interface reacquired, a understandable command line would do. PDF toolkit is this.
apt-get install pdftk
pdftk A=file1.pdf B=file2.pdf cat A1 B2 A2 B1 output output.pdf
This will make an PDF document “output.pdf” with four pages. Page 1 in output.pdf being the first page from file1.pdf, page 2 being the second page from file2.pdf and so on.