Open the Share dialog in one of the following ways:
While viewing a list of documents, tap under the document.
While viewing a message with a document, tap under the message, then tap Share.
While viewing the document, tap in the action bar to display the actions menu, then tap Share.
A list of applications appears.
Tap the application you want to copy the document to.
Tap Always if the application is the one you will always use; tap Just Once, to choose an application each time you share a document.
Alternately, you can share the document while viewing it: