Tamas,
Tamas wrote: > > *Originally I planned to implement full version history in only one pdf > and certify the (any kind of) modifications with signatures. > I will search a work around but please confirm that statement the > previously panned implementation (*) is impossible with itext (or with pdf > at all). > I'm afraid your description is a bit too vague to confirm anything. Tamas wrote: > > The generation number is still not clear for me. You mentioned: > > "I'm afraid, iText does not itself generate objects with generation > numbers greater than 1. Hardly any PDF tool does, by the way." > > [...] > > Page 41. about gereration number: > "Except for object number 0, all objects in the cross-reference table > shall initially have generation numbers of 0. When an indirect object is > deleted, its cross-reference entry shall be marked free and it shall be > added to the linked list of free entries. The entry’s generation number > shall be incremented by 1 to indicate the generation number to be used the > next time an object with that object number is created. Thus, each time > the entry is reused, it is given a new generation number. The maximum > generation number is 65,535; when a cross-reference entry reaches this > value, it shall never be reused." > There you are, everytime an entry is reused, it is given a new generation number. But considering the range for object numbers there is no need for reusing used object numbers, you can easily use a completely unused one. Additionally, while changing a document in append mode hardly any software cares to find out whether any indirect objects it removes a reference to now is completely unreferenced. Therefore fairly often the list of free objects is not used at all. Tamas wrote: > > From you: > "The generation number does not reflect the document revision the object > belongs to. The revision an object belongs to only depends on its position > in the file. " > > So what does it mean? Only the IText does not support the generation > higher number than 1 or something else? What is the generation number is > used for? > Currently I hardly see a use for positive generation numbers. Adobe doesn't seem to, either, as they did not even consider them when introducing cross reference streams. I tend to see them as a historical relict which must be supported for compatibility while reading a PDF; while writing, though, they need not be used. Regards, Michael. -- View this message in context: http://old.nabble.com/Append-existing-signed-PDF-with-content-in-such-way-signature-stays-valid.-%28generation-next%29-tp26132337p26157721.html Sent from the iText - General mailing list archive at Nabble.com. ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference _______________________________________________ iText-questions mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/itext-questions Buy the iText book: http://www.1t3xt.com/docs/book.php Check the site with examples before you ask questions: http://www.1t3xt.info/examples/ You can also search the keywords list: http://1t3xt.info/tutorials/keywords/
