On an iPad or iPhone you can lock PDF files with a password. All that you have to do is put a PDF document into the Files app, open the app and use the Lock PDF feature to set up a password. This option adds an extra layer of security for your sensitive documents.

• Open Files and find you PDF document
• Tap on the document’s thumbnail to open it.
• Use the Share icon.
• Select Lock PDF.
• Type a Password and verify it. Tap Done. (Make sure to tap done again at the top left corner.)