To sign a PDF, click Sign on the Tools tab. An Open File window appears. Select a PDF file, or click Cancel if you'd rather select a PDF later. The Sign PDF window opens. You can now click Browse to select another PDF file to sign.

Defining the area for your signature

Click Place Signature. Using the mouse in the right preview panel, drag to select the area for the signature. Alternatively, you can click an existing signature field.

Selecting a digital ID

A new window opens to allow you to add your digital ID to the signature area. At the top of the window, you'll see a drop down list of all the digital IDs (certificates) registered on your computer. You can create a self-signed digital ID or use a digital ID purchased from a third party certificate authority. Read more about obtaining a digital ID.

Changing the appearance of your signature

Next you can change the appearance of your digital signature, which can contain your name, date, reason for signing, and location. You can also select an image for your signature. It is a good idea to use an image file scanned from your actual signature. All the popular image file formats are supported.

Here you can also select the Lock the document option to disallow any future changes to the document after it has been signed.

Signatures Visibility

Digital signatures can be visible or invisible. Check the Appear on all pages option if you want the signature to be visible on all pages of a document. This is just a matter of visual preference because placing a signature on one page is enough to validate your document.

Check the Invisible option if you want your signature to appear only in the Signatures panel of Adobe Reader.

Check the Visible on print option if you want an invisible signature to be visible when printed on paper.

Saving the signed PDF

When you click Sign, you will be prompted to save the document with the new digital signature.

Removing a digital signature

To remove a digital signature, just open a document in the Sign PDF tool. In the left panel, you'll see a list of all signatures applied to the document. To remove a signature, select it in the list and click Remove. Click Save As to save the PDF.

Placing signature fields for others to sign

If you would like to create a preexisting location for other people to use, first open a document in the Sign PDF tool. Then click the Place Signature Field option, and using the mouse in the right panel, drag to select the area for the signature field.

Applying a signature to multiple PDFs

Click the Sign Multiple Files button, and select all the PDFs you want to sign. Click OK. The New Signature window opens, and you’ll be able to specify the details. Click Sign to digitally sign all the selected PDF documents.

Certifying Signatures

The intention of certifying a document is to prove the identity of where it came from and then restricting what others can subsequently do with the document, for example, changing the content. Signing, on the other hand, means you agree to the content.

A certifying signature is a way to prove the identity of the person who created the document and to restrict what others can do with the document subsequently. A simple signature , on the other hand, is typically used to just approve a document.

There can be more than one signature in a document, but only the first signature can be certifying. For example, the person who created a PDF can sign it with a certifying signature and assign certain permissions, for example, allowing or disallowing changes to the document. Next, people who subsequently read the document can make changes (if allowed) and sign their approval.

To place a certifying signature, select a PDF for signing and click Certify. Next, using the mouse in the right preview panel, drag to select the area for the signature.

A new window opens to allow you to add your certifying signature, much like an approval signature.

The difference is that here you’ll be able to set what actions on the PDF others will be permitted to do. Use the Permitted actions after certifying drop down list.