You can share your PDFs with other people or apps.
Open the PDF document you would like to share.
Tap the share button in the action bar on the top of the screen.
Select an the app extension from the share sheet, or select the "Open In" extension to see a list of apps that can open the PDF. Some extension have options. For example: the note to add the PDF to in Apple's Notes app.
Tap "Save" or "Done" to complete the action.