Applying a digital signature to a PDF document demonstrates that a particular person has read and approved of the document. Anyone opening a PDF in Adobe Acrobat can add a signature, but users of the less full-featured Adobe Reader normally cannot. If you have Acrobat, however, you can change a PDF's settings to allow signing by Reader users.
Open your PDF in Adobe Acrobat, by double-clicking it or by using Acrobat's "Open" command in the "File" menu.
Open the "Advanced" menu and click "Extend Features in Adobe Reader."
Click "Save." Adobe Reader users opening your PDF will now be able to apply digital signatures.