Vía AccesoWeb 2.0 by PDF Hammer is a website that allows you to edit your PDF files online for free. You don’t need to install any additional software, you can edit PDF documents right now inside your browser. Once you start, you will be able to upload one or more PDF files into your project, arrange the pages in any order you wish, and delete any pages you don’t want.
For example, you can create a PDF document that has the cover page of one PDF file, followed by all of the pages of another PDF file, and finally followed by the back-cover page of the first file.
Fuente: [ PDFHammer, vía acceso web 2.0]