Click More options and Select all permissions that you want others to have on your document. By default none as selected (most secure, most restrictive).
Here’s the available permissions:
Modifying - Modify the contents of the document by operations other than those controlled by other permissions.
Copying text or graphics - Copy or otherwise extract text and graphics from the document, including extracting text and graphics.
Printing - Print the document (possibly not at the highest quality level, depending on whether ‘High Resolution Printing’ is also selected).
High resolution printing - Print the document to a representation from which a faithful digital copy of the PDF content could be generated. When this permission is not selected and only 'Printing’ permission is, printing is limited to a low-level representation of the appearance, possibly of degraded quality.
Filling forms - Fill in existing interactive form fields (including signature fields).
Commenting - Add or modify text annotations, fill in interactive form fields, and, if 'Modifying’ permission is also selected, create or modify interactive form fields (including signature fields).
Insert, rotate or delete pages - Assemble the document (insert, rotate, or delete pages and create bookmarks or thumbnail images), even if 'Modifying’ permission is not selected.
You should know that these permissions are not enforced by all PDF readers, so they are not 100% safe.