PDFHammer is an online tool that lets you edit PDF documents online. You can upload a pdf file and rearrange the pages of the file or delete some pages and export as a new pdf document.
You can also upload multiple pdf files and edit them by deleting pages or rearranging pages from both files in to one and publish as a new file. This is a good way if you want to merge pdf documents.
PDFHammer is free to use, and will have some more features like rotating the pages, adding watermarks and stamps to pages in the near future.