PDFsam (short for PDF Split and Merge) is an open-source tool which provides you with a great solution for dealing with large documents. You should also keep in mind that the free version of the service limits you to 100 MB or 100 pages and will 'forget' your document after 7 days. As far as disadvantages go, there is no undo option (the only thing you can do is clear all the changes) and you can't copy-paste the text from your document.
Additionally, you can also rotate, crop or deskew any page from the PDF. This service allows adding texts, images, drawings or links to your documents and highlight or place sticky notes on the fragments which are important to you. PDF Escape is a web-based tool which allows you to perform a wide variety of changes to your PDF files. Let's start things off with a great alternative that you don't even need to install.
