Hack 66 Copy-Protect Your PDF

Control how far your document can wander by making it difficult to copy.

A large document represents a great deal of work, and PDF is a good way to distribute large documents. Sometimes, it is too good. Perhaps your readers are paying customers, and you don't want them to make copies for their friends. Perhaps you want people to read your work only from your web site, not from a downloaded copy. These kinds of controls go beyond standard PDF security [Hack #52] . This hack discusses some solutions.

5.17.1 Low Tech: Print Editions

Copying and sharing print editions of your document would be too much trouble for most readers. Your price for this security is the cost and trouble of production and shipping. However, readers might prefer a print edition, such as the one shown in Figure 5-15, in which case you are also adding value to your work. [Hack #29] discusses how to create print-on-demand (POD) books. Print editions are vulnerable to being converted to unsecured PDF by scanning and OCR.

Figure 5-15. Old-fangled copy protection

5.17.2 Online Reading Only

Another idea is to prevent the reader from ever downloading your PDF. A single PDF can always be downloaded. So, burst your document into individual PDF pages and then wrap them in our HTML skins [Hack #71] . When you burst the PDF, supply additional security settings [Hack #52] for the output pages so that the reader won't be able to easily reassemble them. For example:

pdftk doc.pdf burst encrypt_128bits owner_pw 23@#5dfa allow DegradedPrinting

After integrating your document into your web site, you can employ user accounts, passwords, and other common security devices for enforcing access permissions.

Skinned PDFs are vulnerable to being copied from your site using a recursive HTTP robot. The result would be an exact copy of your site's pages (PDF and HTML) on the user's local machine.

5.17.3 Chain the PDF to the User's Machine

Digital Rights Management (DRM) tools give you fine-grained control over how and when the reader can use your document. Typically, a reader downloads the full PDF, but he can't read it until he purchases a key. After he makes the purchase, a key is created that can open that PDF only on that computer. Some readers find this model too restricting.

DRM software vendors include Adobe (PDF Merchant), FileOpen Systems, Authentica, and SoftSeal. Their tools tend to be too expensive for the casual user. Consider partnering with a distributor or a self-publishing service [Hack #29] .