PDF Expert from Readdle can be used with My Docs Online to sync and sign pdf documents on an iPad or iPhone, using these basic steps:

• Install PDF Expert (available from the App store).
• Set up a WebDAV connection to your My Docs Online account in PDF Expert.
• Open your My Docs Online account and select the folder or folders containing documents to be signed and select “Sync”.
• In PDF Expert’s synced folders open the file to be signed.
• Using the “Sign Tool” create a signature using your finger or a stylus (one time only, later you can just select it).
• Tap the location where the signature is to be applied. Position the signature and resize as desired. Close the PDF document to automatically sync it back to My Docs Online.

For a more detailed step-by-step guide including screenshots, see this pdf document.

You can also find additional information on Readdle’s PDF Expert support pages.