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PDF 2.0 (ISO 32000-2): Deprecated Features

Several features from earlier PDF versions are declared as deprecated in PDF 2.0. »Deprecated« means that a feature should not be used when creating new PDF 2.0 documents. However, it may still be supported in viewers for processing existing documents or even PDF 2.0 document which still contain deprecated features.

The document info dictionary has been available as a container of metadata for a long time. Document info entries such as Title, Author, Subject, Keywords played an important role even after the introduction of the more general XMP metadata framework. However, the difficult relationship and synchronization of document info entries and XMP properties caused a somewhat rough start for the PDF/A standard as can be seen in the evolution of PDF/A standards. While PDF/A-1 allows document info entries to be present, it requires them to be synchronized with XMP metadata according to a set of rules. Since the synchronization caused a lot of headache, PDF/A-2 and PDF/A-3 require conforming PDF/A readers to completely ignore document info entries in favor of XMP. Consequently, PDF 2.0 declares document info entries as deprecated except for the CreationDate and ModDate entries.

XFA forms are no longer part of PDF 2.0. Actually, XFA hasn’t really been a part of the PDF file format, but rather a separate format of its own which has been attached to PDF. The vast majority of available PDF software doesn’t support XFA forms anyway.

The use of Flash/Shockwave, introduced with PDF 1.7 extension level 3 and Acrobat 9, is not part of PDF 2.0. This affects Flash-based navigators for portfolios; these have been replaced by a set of of predefined navigator layouts. Also affected are multimedia applications of Flash, such as Flash-based video.

Classical PDF form fields (also called AcroForms) can have a description of their visual appearance attached in addition to the actual form field contents. If this so-called appearance stream is missing, the viewer must create it upon opening the document. By omitting appearance streams the PDF producer is relieved from creating them, but this also creates ambiguities regarding the document’s visual representation and problems when digitally signing the document. For these reasons PDF/A requires form field appearances to be present. PDF 2.0 follows this direction and deprecates the construct NeedAppearances true.

Weak encryption schemes and algorithms for password security are deprecated. This includes the RC4 algorithm as well as a weak scheme based on AES-128 encryption (while the AES-128 algorithm itself is still considered secure, it is used in a weak scheme in PDF and therefore deprecated). Only AES-256 encryption used in a secure encryption scheme is encouraged in PDF 2.0.

Similarly, certificate security should refrain from using any other algorithm than AES-256. DES and other algorithms are deprecated in PDF 2.0.

Several old signature flavors are deprecated: signatures with the SubFilter values adbe.x509.rsa_sha1 and adbe.pkcs7.sha1 should no longer be created in favor of the modern PAdES signatures (SubFilters adbe.pkcs7.detached and ETSI.CAdES.detached.

Movie and sound annotations are deprecated. Unlike mentioned in some publications, this doesn’t mean that interactive media are no longer supported in PDF 2.0. Instead, it simply means that the older concepts used in the Movie and Sound annotations have been replaced with the more powerful RichMedia annotation type introduced with Acrobat 9. Similarly, the deprecated Movie and Sound actions are replaced with the RichMediaExecute action.

Several PDF syntax features without any practical use have been deprecated, including the ProcSet array, internal names for XObjects and fonts, and CharSet and CIDSet entries. Note that while PDF/A-1 requires CharSet and CIDSet, this requirement has already been relaxed in PDF/A-2 and PDF/A-3.

A concept called Open Prepress Interface (OPI) has been specified by Aldus for the PageMaker product at the end of the 1980s. It was used in PostScript output to replace low-resolution image placeholders with their high-resolution counterparts. Although the concept has been carried over to PDF, it never really enjoyed much support among vendors and therefore has been declared as deprecated.

Usage rights have been used to Reader-enable PDF documents, i.e. a digital signature which activates additional processing tools in a PDF consumer. The concept of usage rights is deprecated in PDF 2.0.