Unite PDFs:

	pdfunite IMG* union.pdf


Rotate 90 degress clockwise:
	
	pdftk union.pdf cat 1-endeast output 1.pdf


Split vertically (use -x for horizontal split):
	
	mutool poster -y 2 1.pdf


Split into separate files, one page per file:

	pdfseparate out.pdf %d.pdf


Check Djvu metadata:
	
	djvused -e print-meta book.djvu