PDFsam

PDFsam Basic is a free, open source, multi-platform software designed to:

Merge PDF files (the entire documents or selected page ranges), retaining or discarding bookmarks, acroforms and generating or not a table of contents.
Split PDF files by pages (odd, even, single pages, etc.).
Extract a selection of pages from a PDF file.
Split PDF files by size.
Split PDF files by bookmarks level.
Rotate PDF files in batch.
Mix multiple PDF files together taking pages alternatively from one and the other.

PDFsam Enhanced and Visual are PDFsam Basic freemium siblings providing additional functionalities like modify, convert, review, sign, fill forms, encrypt, crop, split by text, etc.