If you have the need to split up a PDF, i.e. one big handout into bite sized chunks for students. pdftk is your friend, so to split off the appendix of l4fluidsnotes.pdf which is on pages 125-130 the following works:
pdftk A=l4fluidsnotes.pdf cat A125-130 output appendix.pdf
The only difficulty is making sure you know which page numbers you need, there is often a mismatch between the page number shown and the ones you need as the contents page often isn’t counted.