The PDF/X-3 standard

This level of the PDF/X standards had a relative success in Europe but very little in the United States and other markets. Its main difference with PDF/X-1a is that it is the beginning of support for RGB, colour management and device-independent colours.

PDF/X-3 was made obsolete by the emergence of PDF/X-4 in 2008, against which it does not have any major advantage. It was published in 2002 and had a revision in 2003. Therefore it has two revisions:

• "PDF/X-3:2002"
• "PDF/X-3:2003".

For practical purposes there is not much difference between them.

Prohibitions and obligations

The prohibitions and obligations are what define a PDF/X level. These are the main ones in PDF/X-3. Some of the prohibitions are due to the fact that the features in question did not yet exist in PDF format when the standard was defined.

• PDF format level: The use of a PDF format level higher than 1.3 is forbidden (2001 revision). In the 2003 revision, level 1.4 is allowed, but in an extremely limited way (most of its features are not used). In both revisions, the use of level 1.2 is allowed (although not recommended).
• The use of features not included in the PDF format definitions of the level in use (e.g. third-party extensions) is prohibited.
• Security: No access restrictions (passwords of any kind, etc.) are allowed. No encryption may be used.
• Self-contained: All needed elements must be inside the document. The use of external linked elements (images and fonts) and OPI is not allowed.
• Attached files are not allowed (unless they are fonts or images that are a direct part of the content).

• Metadata: Every document must have the following metadata in its info dictionary:

  • Internal tags ("GTS_PDFXVersion" and "GTS_PDFXConformance") that identify the level and revision of the PDF/X standard for which the document was created.
  • Its creation date.
  • The modification date.
  • The document title.
  • A trapping key indicating whether the document has been trapped or not. The value "unknown", which can be used outside the PDF/X standards, is not allowed.

  Besides, every document must have a unique document ID.

• Interactivity: The presence of interactive elements (JavaScript, active forms, Flash, etc.) and multimedia (videos, sound, 3D, etc.) is forbidden.

  The use of non-printable comments within the printable area is prohibited.

• Optional content: Layers are not allowed.

• Fonts: All fonts used must be embedded fully or partially (as subsets, at least all characters used).

  Embedding of OpenType fonts is forbidden.

• Transparencies: Transparencies (blending modes such as multiply, raster, etc.) are not allowed. All content must be flattened.

• Inks and colours: Besides the colours supported in the previous level  (DeviceGray, DeviceCMYK and spot colours defined as Separation or DeviceN colour modes), the use of calibrated, device independent colour modes is supported in this level (CalGray, CalRGB, with ICC colour profiles (Level 2 colour profiles only) and Lab). Besides, the use of DeviceRGB is allowed as well.

  This enlargement of supported colour modes has some limitations, which are explained below, when discussing output intents.

  Vector gradients (smooth shading) and patterns also support these new colour modes.

  If spot colours are used, the values of the alternate colour space of each one of them must always be the same in all the cases it is used.

  The alternative colour space of a spot colour can now be defined in Lab mode (in addition to DeviceCMYK and DeviceGray).

• Compression: Only a few compression algorithms are supported: JPEG, JBIG2, JPEG2000, ZIP, CCITT (type 3 and 4), Run-Length (RLE), and ASCII85. LZW is prohibited.

  Objects streams cannot be compressed.

• Images: Images with more than 8 bits depth per pixel are not allowed.

  The use of alternative images is not forbidden, but they must not be the default for printing.

• Pages and dimensions: Page geometry must be defined using the MediaBox, TrimBox or ArtBox. The BleedBox is optional and must be only used if there is a bleed printing.

  Page boxes must be correctly nested.

  The simultaneous presence of TrimBox and ArtBox is prohibited. There can be only one.

  Different page sizes are not allowed in a multi-page document (any box page must be the same  size throughout the whole document).

• Prepress: Preseparated pages (where colour separation has already been carried out and each page represents a plate) are prohibited.

  PostScript code and transfer functions are not allowed.

  The use of halftones other than type 1 or 5 (out of the ten defined in the PostScript specifications) and some minor details related to halftones are prohibited.

  The use of scaling factors is forbidden.

• Printing aim: It is mandatory to report the final printing system for which the document has been prepared. This must be done through a structure called "output intent", which is included in the catalog dictionary (and explained in more detail on another page). It is the only place where this information is provided.

  It is forbidden for a document to have more than one output intent (which PDF format does allow).

  It is possible to specify the final printing system just with a reference to a set of standardised printing conditions, such as "FOGRA27" and a colour register (such as www.color.org).

  As device independent colours are allowed, the output intent in this level of PDF/X is more important than in PDF/X-1a, as it is the method which the receiver has to know which is the final intended printing system.

  Chromatic restrictions on the output intent: The possibility of using uncalibrated and device-independent colour elements in the same document imposes some restrictions on the output intent:

  • If a document contains DeviceRGB elements, it cannot contain any other colour mode and the printing purpose must be an RGB profile (of type "ptr").
  • If DeviceCMYK is used in the document, the printing purpose profile must be CMYK (it cannot be either RGB or greyscale).
  • If all the elements of the document are DeviceGray, the printing purpose profile can be grayscale or CMYK.
  • If calibrated or device-independent colours are used (Lab, CalGray or with an ICC colour profile), there is no restriction on the profile of the output intent, which can be greyscale, CMYK or RGB.
  • If spot colours are used in Separation or DeviceN colour modes, there are also no restrictions on the printing purpose profile, which can be grayscale, CMYK or RGB.
  • The exception is that if classic spot colours are used (those with their alternative colour space in DeviceCMYK), the profile of the output intent must be CMYK (it can be referred to. It is not mandatory to include it).
  • If the alternative colour space definition for spot colours is DeviceGray, this restriction does not exist.
  • If the alternative colour space of a spot colour is device independent (Lab), a colour profile must be included in the output intent. A simple reference to it is not enough.
  • But if a colour profile is used (referenced by name or embedded in the document), that colour profile must be a Grayscale, RGB or CMYK one, printer's ("ptr") type and no higher than level 2 of the ICC specifications.

Standards that define it

PDF/X-3 is specified in the standards ISO 15930-3:2002 e ISO 15930-4:2003.