14. A system comprising: a processor; and a non-transitory computer readable medium having stored thereon instructions that, when executed by the processor, cause the processor to: receive, from a user operating a client computing device, an electronic document; convert the electronic document into a standard image format; cause the converted electronic document to be displayed to the user via the client computing device; receive, from the user, user input for adding an electronic signature to the electronic document, the receiving comprising: generating a unique identifier for the user; instructing the user to capture an image of the user's signature using a camera of a smartphone; instructing 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 the email message transmitted by the user; associating the email message with the user based on the unique identifier included in the email's subject line; extracting the image of the user's signature from the email message; generating 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 one or more commands from the user via manipulation of the first, second, and third controls; modifying the image of the user's signature based on the one or more commands; and saving the modified image of the user's signature as the electronic signature; generate an annotated version of the electronic document that includes the electronic signature; and send the annotated version of the electronic document to a recipient designated by the user.
14. A system comprising: a processor; and a non-transitory computer readable medium having stored thereon instructions that, when executed by the processor, cause the processor to: receive, from a user operating a client computing device, an electronic document; convert the electronic document into a standard image format; cause the converted electronic document to be displayed to the user via the client computing device; receive, from the user, user input for adding an electronic signature to the electronic document, the receiving comprising: generating a unique identifier for the user; instructing the user to capture an image of the user's signature using a camera of a smartphone; instructing 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 the email message transmitted by the user; associating the email message with the user based on the unique identifier included in the email's subject line; extracting the image of the user's signature from the email message; generating 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 one or more commands from the user via manipulation of the first, second, and third controls; modifying the image of the user's signature based on the one or more commands; and saving the modified image of the user's signature as the electronic signature; generate an annotated version of the electronic document that includes the electronic signature; and send the annotated version of the electronic document to a recipient designated by the user. 15. The system of claim 14 wherein the processor is further configured to: receive user input for adding a checkmark or a text string to the electronic document; and add the checkmark or the text string to the annotated version of the electronic document.