You would need a custom digital signature plug-in. What advantage do you see this method having over a static signature appearance?
Ignore that last comment/question, I misunderstood what you wanted.
Are you using Acrobat or Reader and which version.
Im using Adobe acrobat Pro (Acrobat XI version 11.0.4)
Do you think this is possible?
In order for this to work the file cannot have any existing signature fields. If the document author added a signature field then they intended for the recipients to create a certificate based digital signature, not what you are looking to do. If however there are no digital signature fields then this is pretty easy.
With the file open click on Sign on the toolbar to open the Sign panel. The panel is divided into three section and you need to open (expand) the top section I Need to Sign.
Click on the Place Signature button button. That will bring up the Place Signature dialog that looks like this:
Select the Draw my signature radio button and then use your mouse to draw a signature.
Click the Accept button
Now your cursor is your signature. You can move the mouse to where you want to place the signature and with one mouse click it's there.
Unless you clear the signature from here on out every time you select the Place Signature button the cursor turns into your signature. You only need to create it once.
I hope this helps,
You can create your own stamp from any image (or PDF) file that you have...
Go to Comment - Stamp - Custom Stamp - Create Custom Stamp, then select the file, give it a name and you'll have direct access to it from the Stamp tool.