A method is provided of associating in computer memory (i) a digital electronic version of printed human-discernible content of a printed document comprising a sheet having a machine-readable pattern adapted to enable the position of a digital pattern reading device to be determined and said human-discernible content with (ii) the identity of a sheet upon which the content is printed, the method comprising: printing the content onto a sheet using a printer, said sheet comprising a pre-patterned sheet that has been pre-printed with said pattern; transferring a machine-readable identity code between said printer and said sheet at around the time of printing said content; and storing a correlation between said identity code and said digital electronic version in computer memory.