Adobe Acrobat Reader mobile app allows you to protect your PDF file with password. Subscribers to Adobe Acrobat Premium or Adobe Acrobat Pro DC can password protect PDFs by setting a document open password.
Note: Only document open password can be setup using mobile app. For permission password, you would be required Acrobat DC desktop application.
Things to keep in mind, when creating password for a PDF:
The app creates a file copy named “<the file name>_protected” and saves that file to the Document Cloud. It does not protect or change the original file.
Actions which change the file are blocked on mobile devices, including Fill & Sign, commenting, and editing.
You can use the restricted features with desktop Acrobat.
You can remove the password with desktop Acrobat (you must know the original password).
There is no separate password for edit. If a user can open a file, they can edit the file.
To password protect a file from within an open PDF or from any file list: