1. A method comprising: receiving, by a server computer system, an electronic document from a user operating a client computing device; converting, by the server computer system, the electronic document into a standard image format; causing, by the server computer system, the converted electronic document to be displayed to the user via the client computing device; receiving, by the server computer system from the user, user input for adding an electronic signature to the electronic document, the receiving comprising: generating, by the server computer system, a unique identifier for the user; instructing, by the server computer system, the user to capture an image of the user's signature using a camera of a smartphone; instructing, by the server computer system, the user to transmit, from the smartphone, an email message to a predefined administrative email address, wherein the email message includes the image of the user's signature as an email attachment and includes the unique identifier in the email's subject line; receiving, by the server computer system, the email message transmitted by the user; associating, by the server computer system, the email message with the user based on the unique identifier included in the email's subject line; extracting, by the server computer system, the image of the user's signature from the email message; generating, by the server computer system, a user interface that presents the image of the user's signature to the user and that includes: a first control for cropping the image of the user's signature; a second control for adjusting contrast of the image of the user's signature; and a third control for rotating the image of the user's signature; receiving, by the server computer system, one or more commands from the user via manipulation of the first, second, and third controls; modifying, by the server computer system, the image of the user's signature based on the one or more commands; and saving, by the server computer system, the modified image of the user's signature as the electronic signature; generating, by the server computer system, an annotated version of the electronic document that includes the electronic signature; and sending, by the server computer system, the annotated version of the electronic document to a recipient designated by the user.
1. A method comprising: receiving, by a server computer system, an electronic document from a user operating a client computing device; converting, by the server computer system, the electronic document into a standard image format; causing, by the server computer system, the converted electronic document to be displayed to the user via the client computing device; receiving, by the server computer system from the user, user input for adding an electronic signature to the electronic document, the receiving comprising: generating, by the server computer system, a unique identifier for the user; instructing, by the server computer system, the user to capture an image of the user's signature using a camera of a smartphone; instructing, by the server computer system, the user to transmit, from the smartphone, an email message to a predefined administrative email address, wherein the email message includes the image of the user's signature as an email attachment and includes the unique identifier in the email's subject line; receiving, by the server computer system, the email message transmitted by the user; associating, by the server computer system, the email message with the user based on the unique identifier included in the email's subject line; extracting, by the server computer system, the image of the user's signature from the email message; generating, by the server computer system, a user interface that presents the image of the user's signature to the user and that includes: a first control for cropping the image of the user's signature; a second control for adjusting contrast of the image of the user's signature; and a third control for rotating the image of the user's signature; receiving, by the server computer system, one or more commands from the user via manipulation of the first, second, and third controls; modifying, by the server computer system, the image of the user's signature based on the one or more commands; and saving, by the server computer system, the modified image of the user's signature as the electronic signature; generating, by the server computer system, an annotated version of the electronic document that includes the electronic signature; and sending, by the server computer system, the annotated version of the electronic document to a recipient designated by the user. 6. The method of claim 1 further comprising, prior to sending the annotated version of the electronic document, receiving user input for positioning the electronic signature within the annotated version of the electronic document.