Many pdf file attributes are launched merely by adding new entries to present dictionaries. Earlier editions of viewer products do not discover the existence of such entries and behave just as if they had been not there. this type of new attributes are as a result both forward- and backward-compatible. Likewise, adding entries not described in the pdf file specification to dictionary objects does not have an effect on the viewers’ behavior. (See Appendix E for info regarding how to pick essential names that come about to be compatible with potential editions of PDF.)
In some cases, a manufacturer new function is not possible to ignore, due to the fact carrying out so would preclude some important operation just like viewing or printing a page. For instance, if a page’s content material stream is encoded with some new sort of filter, there is no method to view or print the page, even although the content material stream (if decoded) would be perfectly understood through the viewer. There is tiny option but to provide an error in cases like these. this sort of new capabilities are forward-compatible but not backward compatible.
In several cases, new capabilities are defined in a very way that earlier viewer designs will ignore, however the output might be degraded in some way with no any error indication. The most considerable instance of this really is transparency. All from the transparency features launched in pdf file 1.4 are defined as new entries in present dictionaries(including the artwork point out parameter dictionary). A viewer that does not understand transparency treats transparency team XObjects as though they had been opaque form XObjects. This is generally a considerable sufficient deviation through the intended habits that it is worth pointing out being a compatibility concern (and so is covered in implementation notes on this appendix).
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