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Section H.2. Feature Compatibility

H.2. Feature Compatibility

Many PDF features are introduced simply by adding new entries to existing dictionaries. Earlier versions of viewer applications do not notice the existence of such entries and behave as if they were not there. Such new features are therefore both forward- and backward-compatible. Likewise, adding entries not described in the PDF specification to dictionary objects does not affect the viewers' behavior. (See Appendix E for information on how to choose key names that are compatible with future versions of PDF.)

In some cases, a new feature is impossible to ignore, because doing so would preclude some vital operation such as viewing or printing a page. For instance, if a page's content stream is encoded with some new type of filter, there is no way to view or print the page, even though the content stream (if decoded) would be perfectly understood by the viewer. There is little choice but to give an error in cases like these. Such new features are forward-compatible but not backward-compatible.


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