(Required if RF is present; PDF 1.3; amended to include the UF key in PDF 1.7) A dictionary containing a subset of the keys F, UF, DOS, Mac, and Unix, corresponding to the entries by those names in the file specification dictionary. The value of each such key is an embedded file stream (see Section 3.10.3, “Embedded File Streams”) containing the corresponding file. If this entry is present, the Type entry is required and the file specification dictionary must be indirectly referenced. (See implementation note 46in Appendix H.) Note: It is recommended that the F and UF entries be used in place of the DOS, Mac, or Unix entries.

(Required if the DOS, Mac, and Unix entries are all absent; amended with the UF entry for PDF 1.7) A file specification string of the form described in Section 3.10.1, “File Specification Strings,” or (if the file system is URL) a uniform resource locator, as described in Section 3.10.4, “URL Specifications.” Note: It is recommended that the UF entry be used in addition to the F entry. The UF entry provides cross-platform and cross-language compatibility and the F entry provides backwards compatibility

(Required if an EF or RF entry is present; recommended always) The type of PDF object that this dictionary describes; must be Filespec for a file specification dictionary (see implementation note 45 in Appendix H).