I want to password-protect a PDF document. Can I do that with PDFpen?

Yes, there are two types of passwords you can apply in PDFpen(Pro): User Password, and Owner Password.

User Password: To apply a User Password, choose File > Save As (hold down Option key for Save As to appear if you are working with a later OS e.g. Lion, Mountain Lion, Mavericks and higher). Then, under the Encryption drop-down menu, choose an Encryption level. User Password restricts access to the entire form such that the user needs to enter a provided password in order to open the document.

Owner Password is an advanced feature available in PDFpenPro beginning with v.6x. Owner Password restricts user interaction with specific aspects of the document. If you applied Owner Password, this would not prompt the user for a password upon opening the document. The user can still access the document. What is limited, are specific document actions such as printing, editing the document etc. Owner Password is applied in Inspector. You can find more information on Owner Password in our Help manual.