Remove signatures that grant permissions. If you want to modify (beyond adding signature fields, signing signature fields, and filling in form fields) a PDF document that has permissions granted to Adobe Reader by digital signatures, you have to remove those signatures first by calling this function. That action will remove the permissions for Adobe Reader but enable modifying the document without breaking those signatures. Permissions granted via encryption are not altered by this function. This function is available for PDF documents only.

public void removePermissions(
	int flags
)