While conforming PDF/A documents are PDF documents, not all PDF viewers are necessarily conforming PDF/A viewers. This is caused by additional requirements imposed on PDF viewers by the PDF/A standard. The concept of a »PDF reader« as defined in the standard includes tools for viewing the contents of a document interactively, but also encompasses non-interactive tools such as a Raster Image Processor (RIP). While basic rendering of a document screen or paper is specified in ISO 32000-1, PDF/A further qualifies several aspects of rendering including the following:

• While plain PDF viewers are free to ignore ICC-based color specifications and may use the alternate color space instead, conforming PDF/A readers must always use the device-independent color information.
• Conforming PDF/A readers must ignore certain device-specific information in a document, e.g. black generation and undercolor removal (these are device-specific features for the graphic arts industry).
• Conforming PDF/A readers are not allowed to render documents with fonts which may happen to be available locally on the viewing system. Instead, only the fonts embedded in the document are allowed for rendering.
• Starting with PDF/A-2, conforming viewers must ignore old-style document information fields and must fully rely on XMP metadata.