PDF

PDF (Portable Document Format) is a platform-independent page description file format designed for platform exchange. It may contain text, vector graphics and bitmaps.

For detailed information about PDF, browse the Adobe Internet site.

Reading PDF Files

In Acrobat 4.0:

  • The minimum allowed page size is 3 x 3 units in default user spacing (i.e. approximately 0.04 x 0.04 inches).
  • The maximum allowed page size is 14,400 x 14,400 units (i.e. 200 x 200 inches).

If the page size is beyond these limits, Acrobat Reader might not be able to correctly read the page. However, this might not apply to other PDF reading applications.

PDF/A

PDF/A is a file format intended to be suitable for long-term archiving of electronic documents for which PDF is already being used.

It is based on the PDF Reference Version 1.4 from Adobe Systems Incorporated and is defined by the ISO standard [ISO 19005-1:2005] entitled Document Management - Electronic document file format for long-term preservation - Part 1: Use of PDF (PDF/A-1).

PDF/A-1 files must contain:

  • Embedded fonts (including standard PDF PostScript fonts)
  • Device-independent colors
  • XMP metadata ("Extensible Metadata Platform"): a common standard designed by Adobe to enable multiple applications to work with metadata.

PDF/A-1 files do not contain:

  • Encryption
  • LZW compression
  • External references
  • Transparency
  • Multimedia
  • JavaScript.

The ISO standard [ISO 19005-1:2005] specifies two compliance levels for PDF/A-1:

  • PDF/A-1a: complete compliance with [ISO 19005-1:2005] which requires the document structure to be included.
  • PDF/A-1b: mininum compliance to ensure reliable reproduction of the document's visual appearance in the future.

sRGB ICC Profile

sRGB stands for "Standard RGB" and is a standard RGB color space created by HP and Microsoft.

An ICC profile is an ISO-approved color management standard
published by the International Color Consortium (ICC). This aim of this profile is to keep an image color true when converted between native device color spaces and device-independent color spaces.

The ICC profile embedded in the PDF/A file is always a sRGB color profile so that colors are device-independent.

Fonts Forbidding Embedding

PDF/A standards require all used fonts to be embedded in the PDF file.

However, some TTF/OTF fonts do not allow embedding. In that case, the Embed font check box is unavailable and a warning message is displayed.

Characters beyond ASCII printable character range (such as Chinese, Japanese, Korean and other East Asian text) require the font file to be embedded into a PDF file. If the font file is not embedded, the East Asian characters will not be visible in the .pdf file. Such fonts only display ASCII text.

Standard Type 1 Fonts

Standard Type 1 fonts are not replaced in the PDF file.

When accessing the Advanced Configuration dialog box, you can substitute a font with any of the 14 PDF standard Type 1 fonts:

Times-Roman Helvetica Courier Symbol
Times-Bold Helvetica-Bold Courier-Bold ZapfDingbats
Imes-Italic Helvetica-Oblique Courier-Oblique  
Imes-BoldItalic Helvetica-BoldOblique Courier-BoldOblique  

Usually these fonts are never embedded. As the PDF/A-1b format requires all fonts to be embedded (which is not possible), original fonts are embedded instead.

Note that if the Discretized option is activated for a font, then the corresponding text will not be streamed and the font will not be embedded.

PDF Properties and Font Types

When defining the PDF properties, a font can be Discretized, Substituted, or Not Substituted.

 The following table shows the relation between the PDF font properties and the different font types.

Font Property Can be applied to Embedding Set Behavior in standard PDF Behavior in PDF/A-1b
Discretized All fonts N/A Text string is not saved but text is drawn as geometry Text string is not saved but text is drawn as geometry
Substituted Any font substituted by a TrueType font Yes/No Substituted TTF font is embedded according to the user's choice Substituted TTF font is always embedded
Substituted Any font substituted by a standard Type 1 font N/A Standard Type 1 font is mentioned without embedding the font file Original fonts are always embedded (as explained in Standard Type 1 Fonts)
Not Substituted Any font except:
- Stroke font
- TTF/OTF/TTF fonts for which embedding is not allowed.		 Yes/No (N/A for exceptions) Font is embedded according to the user's choice Font is always embedded.
Except for Stroke and TTF/OTF/TTC fonts for which embedding is not allowed, text is discretized

PDF Properties in Acrobat Reader

Font properties of PDF documents (especially their name and whether they are embedded or not) can be seen in Acrobat Reader.

To do so, select File > Properties the access the Fonts tab.