PDF Version 1.7 vs Version 2.0: A Comparison

Introduction

PDF (Portable Document Format) has become one of the most widely used file formats for sharing and distributing documents. Over the years, PDF has evolved through multiple versions, each adding new capabilities. The two most significant versions in use today are PDF 1.7, published as ISO 32000-1 in 2008, and PDF 2.0, published as ISO 32000-2 in 2017 (with a second edition in 2020). This article examines the key differences between these two versions and what they mean for users and developers.

Background: How PDF Versions Work

PDF was originally developed by Adobe Systems and went through versions 1.0 to 1.7 under Adobe's stewardship. Each new version corresponded to a new release of Adobe Acrobat. When PDF 1.7 was adopted as ISO 32000-1, it marked the transition of PDF from a proprietary format to an open international standard. PDF 2.0 (ISO 32000-2) was the first version developed entirely within the ISO standardisation process, independent of any Adobe product release.

Key Differences Between PDF 1.7 and PDF 2.0

Encryption and Security

PDF 1.7 supports encryption using 128-bit AES (Advanced Encryption Standard) as well as older 40-bit and 128-bit RC4 methods. PDF 2.0 introduces support for 256-bit AES encryption, providing significantly stronger document protection. Additionally, PDF 2.0 deprecates the older RC4 encryption methods, which are now considered insecure by modern standards.

Digital Signatures

While PDF 1.7 includes comprehensive digital signature support, PDF 2.0 enhances this with better support for PAdES (PDF Advanced Electronic Signatures), aligning with European regulations for electronic signatures (eIDAS). PDF 2.0 also introduces document timestamps and long-term validation (LTV) mechanisms, making it easier to verify signatures years after they were applied.

Removal of Proprietary Features

One of the most notable changes in PDF 2.0 is the removal of several proprietary Adobe technologies:

• XFA Forms: XML Forms Architecture, a complex forms technology developed by Adobe, has been removed from PDF 2.0. The standard AcroForms technology remains the supported method for interactive forms.
• Flash/SWF Content: Rich media annotations based on Adobe Flash have been removed, reflecting the broader industry move away from Flash technology.
• Adobe-specific JavaScript extensions: While core JavaScript support remains, certain Adobe-proprietary extensions have been deprecated.

Tagged PDF and Accessibility

PDF 2.0 significantly improves the Tagged PDF specification, which is critical for document accessibility. Key enhancements include:

• New standard structure types for better semantic markup, including DocumentFragment, Aside, Title, FENote (footnote/endnote), and Sub (subscript).
• Improved handling of pronunciation hints for assistive technologies.
• Better support for mathematical content through MathML structure elements.
• Namespaced structure types, allowing PDF 2.0 to reference structure types from other standards such as HTML.
• More precise requirements for alternative text, actual text, and expansion text.

Associated Files

PDF 2.0 introduces the concept of associated files, which allows source files or related data to be embedded within a PDF and linked to specific objects in the document structure. For example, a chart in a PDF could have an associated spreadsheet file containing the source data. This feature is particularly valuable for engineering, scientific, and archival workflows.

Page-Level Output Intents

In PDF 1.7, output intents (which describe the intended output device and colour conditions) can only be specified at the document level. PDF 2.0 allows output intents to be set on individual pages, enabling documents where different pages are intended for different output conditions, such as a document containing both colour and monochrome pages.

Black Point Compensation

PDF 2.0 adds a black point compensation flag to the graphics state, giving finer control over colour rendering when converting between colour spaces. This is important for maintaining consistent visual appearance in high-quality print workflows.

Geospatial and Measurement Improvements

PDF 2.0 expands support for geospatial features, allowing PDF maps and engineering drawings to carry more precise coordinate system information. Projection types and geodetic data can be specified in greater detail, improving interoperability with GIS (Geographic Information System) software.

Unencrypted Wrapper Documents

PDF 2.0 introduces support for unencrypted wrapper documents, which allow an encrypted PDF to be wrapped inside an unencrypted shell. This enables recipients to see basic information about the document (such as instructions for how to obtain the decryption key) before needing to decrypt the actual content.

Specification Improvements

Beyond new features, PDF 2.0 includes extensive clarifications and corrections to the specification text. Many ambiguities in the PDF 1.7 specification that caused interoperability issues between different PDF tools have been resolved. The PDF 2.0 specification is approximately 1,000 pages long and is significantly more precise in its requirements and recommendations.

Backward Compatibility

PDF 2.0 maintains a high degree of backward compatibility with earlier versions. Most PDF readers can display PDF 2.0 files even if they do not fully support all new features. However, features specific to PDF 2.0 (such as 256-bit AES encryption or new structure types) may not be available in older software. Files that use only features present in PDF 1.7 or earlier can typically be opened by any modern PDF reader regardless of the version label.

Practical Implications

For most end users, the transition from PDF 1.7 to PDF 2.0 is largely seamless. The key practical considerations include:

• Forms: If you use XFA-based forms, you will need to convert them to AcroForms or an alternative technology, as XFA is not supported in PDF 2.0.
• Security: PDF 2.0's stronger encryption options are important for organisations handling sensitive or confidential documents.
• Accessibility: Organisations creating accessible documents will benefit from the improved tagged PDF structures in PDF 2.0.
• Archiving: The PDF/A-4 standard, based on PDF 2.0, provides updated requirements for long-term document archiving.
• Software compatibility: Ensure your PDF tools support PDF 2.0 if you need to use its new features. Most modern PDF applications now offer at least basic PDF 2.0 support.

Conclusion

PDF 2.0 represents a thoughtful evolution of the PDF standard, strengthening security, improving accessibility, removing outdated proprietary technologies, and adding features that support modern workflows. While PDF 1.7 remains widely used and supported, the industry is progressively adopting PDF 2.0, and understanding the differences between the two versions is important for anyone involved in document creation, processing, or archiving.