A method of associating a first electronic document with a second electronic document comprising having a first physical paper identifier (130) having pen-readable coding (12) which codes for an identifier for the first electronic document, and reading the coding of the first electronic document with a pen (20) to acquire information enabling the identity of the first electronic document to be established, and communicating that identity to a computer processor (107), and using the processor (107) to associate the identified first electronic document with the second electronic document.