as portable document format or u201c pdf u201d that allows the data to be displayed in a specified way e g by adobe display software but renders printing the data or reformatting the data difficult or impossible see portable document format reference manual version 1 2 november 1996 adobe systems inc thus the originator of the unencrypted book data e g a publisher can have a high degree of confidence that the integrity of the book data will survive distribution and that the book data will be displayed in accordance with the originator 39 s intent e g in the intended fonts and type sizes and with intended line and page breaks the usage permission transfer procedure may be applied when permission to use a data item is lent e g by a library leased given e g as a birthday present or sold e g by a book retailer if the permission is lent or leased the procedure also specifies that the secret key is associated with matching expiration times 102 s and 102 r e g each corresponding to a two week period at the sender and recipient computers respectively so that the secret key cannot be used and therefore the data item cannot be used at the sender computer until expiration time 102 s is reached and can be used at the recipient computer only until expiration time 102 r is reached.