1. A method implemented in a system comprising a server computer connected with a client computer for personalized display of digital documents by the client to a user, the method comprising: by the server computer: (a) receiving, from the client computer, user interaction information regarding interactions of the user with a plurality of documents, the interactions including one or more types of interactions selected from a group consisting of: opening a document, viewing a page of a document, making a note on a page of a document, printing a page of a document, modifying a page of a document, sharing a page of a document with others, copying or cutting content from a page of a document and pasting it in another document, navigating to a page of a document while viewing another document, and navigating from a page of a document to another document; (b) storing the user interaction information, including a time stamp of each user interaction, in association with a user ID of the user and document IDs of the documents; (c) generating, based on the stored user interaction information including the time stamps, document association information which indicates which documents are related to which documents; and (d) in response to a request from the client computer to open one of the plurality of documents, determining which other documents are related to the document to be opened, and transmitting to the client computer information indentifying such related documents.