A user manipulates a document using a desktop computer with a large screen. Upon deciding to sign the document, the user invokes a “Sign with Mobile” workflow that causes a two-dimensional barcode to be displayed. Using a signature acquisition application executing on his or her smartphone, the user scans the displayed barcode and creates an electronic signature by snapping a photograph of a conventional pen-and-paper signature or by detecting a handwritten signature drawn on a touch sensitive surface. The signature acquisition application sends the resulting electronic signature to the desktop computer, for example via an electronic signature server. The user is then able to apply the electronic signature to the document as desired.