# PDF Differences

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This is a _public_ (repository for responsible reporting of commonly-seen PDF issues. The PDF files in this repository are targeted test files highlighting specific issues seen across multiple widely-used implementations. Implementations at fault will **not** be named or identified.

The issues identified in this repository are **not** intrinsically related to security - they primarily impact portability and interoperability; PDF's "prime directive"!

Detailed documentation for each test case is provided as MarkDown files and in an associated article on https://www.pdfa.org. 

# The PDF test files

* PDF files are as minimal (short) as possible and well-commented internally.

* PDF files are pure text except for the 2nd line comment with 4 binary bytes. This is so they may be easily viewed in text editors and development environments used by software developers. 

* PDF files have valid conventional cross-reference tables with ample whitespace and line-breaks to further enable easy reading.

* PDF header versions are 1.7. These files do not cover new features or change to features introduced in PDF 2.0 unless explicitly noted otherwise.

* PDF files avoid excessive on-page descriptive text as this makes files larger and more internally complex, obscuring the purpose of allowing developers to quickly and easily understand each test case.

* To further ensure rapidity and ease of comprehension, these PDF files purposely do **not** use many "best practices" such as metadata, embedded fonts, device independent color, etc., and they avoid other large data or complex features that inhibit direct inspection in a text editor (such as Linearization, XMP, cross-reference streams, object streams, compacted syntax, etc) unless necessary to the test case.

* Screenshots used in the ReadMe files have been purposely resized to 600 pix wide after capture. Screenshots should **not** be compared at a pixel level to determine correctness (the image processing was a small attempt at trying to stop this)!!

* Correct renderings are always the _last_ image in the MarkDown, encouraging readers to read everything for a full understanding of the correct appearance.

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PDF files are copyright by the PDF Association and distributed under a [Creative Common Attribution 4.0 International (CC BY 4.0) license](https://creativecommons.org/licenses/by/4.0/). Any source code in this repository is licensed under [Apache License, Version 2.0](https://www.apache.org/licenses/LICENSE-2.0.html).