In the second of several PDF security articles, we show you how to prepare a secure document by creating a digital signature.In this lesson, you'll prepare one of your PDFs as if you were going to send to an outside agency for finalization. You've reviewed the document and made required changes, and now you'll sign the revised advertisement electronically.
Signing a document electronically offers several advantages, not least of which is that you can e-mail the signed document rather than having to fax it. (You can even sign PDF documents in a Web browser.)
Although digitally signing a document doesn't necessarily prevent people from changing the document, it does allow you to track any changes made after the signature is added and revert to the signed version if necessary. (You can prevent users from changing your document by applying appropriate security to the document, as you'll see later in this lesson.) Open your file and let's get started.
Creating a Digital ID
A digital ID lets you create a digital signature or decrypt a PDF document that has been encrypted. You can create a digital ID at the same time that you sign a document, but in this lesson you'll create your self-signed digital ID before you sign the document. (You can also get a digital ID from a third-party provider.)
You can create more than one digital ID to reflect different roles in your life. For this section of the lesson, you'll create a digital ID for T. Simpson, director of advertising.
1. Choose Advanced > Security Settings.
2. In the Security Settings dialog box, click Digital IDs in the left pane. Then click the Add ID button ( ).
In this lesson, you'll create a self-signed digital ID. With a self-signed ID, you share your signature information with other users using a public certificate. (A certificate is a confirmation of your digital ID and contains information used to protect data.) While this method is adequate for most unofficial exchanges, a more secure approach is to obtain a digital ID from a third-party provider.
3. In the Add Digital ID dialog box, select Create a Self-Signed Digital ID. Then click Next and click Next again to close the message box. (On Mac OS, you may not see the message box.) (See Figure One.)
If you're working in Mac OS, you may need to skip step 4. If you're working in Windows, you'll choose where to store your digital ID. The PKCS#12 Digital ID File option stores the information in a file that you can share with others.
A Windows Default Certificate Digital ID is stored in the Windows Certificate Store. Because you want to easily share your digital ID with colleagues, you use the PKCS#12 option.
4. Make sure that New PKCS#12 Digital File ID is selected, and click Next. Now you'll enter your personal information.
5. Enter the name you want to appear in the Signatures tab and in any signature field that you complete, and enter a corporate or organization name (if necessary) and an e-mail address.
We entered T. Simpson, Director for the name, Clarity for the Organization Name, and clarity@xyz.net for the e-mail address. Make sure that you select a Country/Region. We selected US - United States.
6. Choose a Key Algorithm to set the level of security. We chose 1024-bit RSA. Although 2048-bit RSA offers more security protection, it is not as universally compatible as 1024-bit RSA.
Now you'll specify what the encryption applies to. You can use the digital ID to control digital signatures, data encryption (security), or both. When you encrypt a PDF document, you specify a list of recipients from your Trusted Identities, and you define the recipients' level of access to the file—for example, whether the recipients can edit, copy, or print the files. You can also encrypt documents using security policies. For this lesson, you'll choose digital signatures.
7. From the Use Digital ID For menu, choose Digital Signatures and then click Next. (See Figure Two.)
Now you'll save and safeguard your information.
8. If you want to change the location where your information is stored, click the Browse button and locate the required folder. For this lesson, you'll use the default.
Now you must set a password. We used Lotion123 as the password. Reenter your password to confirm it. Remember that the password is case-sensitive. Be sure to make a note of your password in a safe place. You cannot use or access your digital ID without this password.
Note: Your password may not contain double quotation marks or the characters ! @ # $ % ^ & * , | \ ; < > _ .
9. Click Finish to save the digital ID file in the Security folder.
In our next security article, we'll show you how to sign your PDF with your new digital signature and add an image to that signature.
Pages 344-346 excerpted from "Adobe Acrobat 7.0 Classroom in a Book." Copyright © 2005. Used with the permission of Pearson Education Inc. and Peachpit.
Document Management 
