PDF supports a set of permissions that allow authors to disable certain actions such as editing, annotating, or printing documents. To prevent accidental changes and respect authors’ wishes, PDF Viewer for iOS comprehensively respects these restrictions since version 4.3.
For documents you have authored, you can add an owner password and set these permissions directly in PDF Viewer before distributing your document. You can also edit permissions for existing documents, if you have the document password. Note that this functionality requires a PDF Viewer Pro subscribtion.
You can also edit PDF document permissions in third party applications such as Adobe Acrobat.