Try these: how do I sign a document in Android, sign a document in Android

To sign a document in android, click on the document waiting for your signature, then click ‘sign’ and the document will open.

Once the document is open, click on the fields necessary to complete the document. When you click on a signature field, you can sign your name in the specified field. You can see how close you are to completing the document by looking at the bar in the upper right corner. Click the check mark in the top right hand corner when you’re all done!