PDFzen is a great free web tool that allows you to edit and sign your PDFs online. This app is integrated with Google Drive which means that you can easily edit the PDFs you have in your Drive. When you are done, you can save your edits back to Drive or download the document as a PDF or generate a link to share via email or social media websites.
http://www.educatorstechnology.com/2014/12/a-handy-google-drive-app-to-edit.html