If you have a PDF file and need to extract a subset of pages, creating a new PDF file with those pages in it, you can do that.
I like PDF Lab‘s PDFtk aka PDF toolkit. This is not OpenSource and there is both a non free pro and free version of it. I’ve tried the free version (example below) and was impressed. Next time I need to do a lot of PDF work I’ll probably fork out the 399 for the pro version. (That’s 399 pennies, quite cheap. It is developed by Sid Steward, the author of PDF Hacks: 100 Industrial-Strength Tips & Tools.
So, for example, I can get pages 11-20 of a larger file called big.pdf extracted into a smaller file called extracted.pdf like this:
pdftk A=bigpdf cat A11-20 output extracted.pdf
That line of code makes almost no sense to me, but it works.
I learned about this tip at a Linux Journal Tech Tip page on extracting pages from a PDF, where you will find several other approaches.