Steps in Adobe Acrobat to create a button that allows a user to upload an image (which can be a signature)

AttachSignatureToPdf.txt

    Open up the Content Panel via Tools > Content Panel
    
    Using the 'Add a button' tool(top-center, immediately above the doc) draw a button to the size the image field needs to be
    
    Double click the button to enter into the button's properties
    
    Go to the Actions tab
    
    Next to Select Action choose 'Run a JavaScript'
    
    Click Add

    Copy & Paste the following JavaScript in the window:

    event.target.buttonImportIcon();

    OK
    
    Go to the Options tab
    
    Under Layout choose 'Icon Only'
    
    Investigate any other options you need then..
    Close