PDF export functionality supports creating archive PDF documents (PDF/A).
PDF/A is a specific version of the PDF format for long-term archival preservation
of electronic documents. This format differs from common PDF format by excluding
all features that can be dangerous for long-term document storage (for example
font linking, encryption, etc.).
PDF/A format is standardized by ISO. ISO requirements for viewer applications
contain color management guidelines, embedded fonts support, and a user interface
for reading embedded annotations.
There are several versions of PDF/A format:
PDF/A-1 — See Part 1: Use of PDF 1.4 of the ISO PDF/A standard.
PDF/A-2 — See Part 2: Use of ISO 32000-1 of the ISO PDF/A standard.
PDF/A-3 — See Part 3: Use of ISO 32000-1 with Support for Embedded Files of the ISO PDF/A standard.
The difference between PDF/A-2 and PDF/A-3 is insignificant for CAD applications,
therefore ODA Platform supports only PDF/A-1 and PDF/A-2 versions.
To specify a version of PDF/A format, the PDF_A_mode enumeration from the PDFExportParams
class is used.
Note: When exporting drawings into archive PDF format,
it is strongly recommended to use the PDF/A-2 version for the following reasons:
PDF/A-1 version does not support layers.
PDF/A-1 version does not support transparency and the MergeControl parameter
is always set to the LinesOverwrite value.
Values of real data type (for example, coordinates) cannot be greater than
32767; therefore, in some cases DPI resolution should be reduced.
Strings (including streams and stream parts) cannot have a size greater
than 64 Kb. This leads to the following disadvantages:
Picture quality is set to the minimum value.
ASCII hex encoding is unavailable.
Flat encoding is enabled to reduce the possibility of issues during the export process.
PDF/A-1 version does not support the measuring feature.
To export to the desired version of PDF/A format, use the setArchived()
method of the PDFExportParams class. To retrieve whether exporting to the archive
PDF format is enabled, and if enabled, which version of PDF/A format is used,
call the archived()
method of the PDFExportParams class.
There are several restrictions and disadvantages of using the PDF archive
format for export:
The ODA Platform does not support TrueType font optimization yet,
therefore the TrueType font optimization flag is switched off if PDF/A support
is applied.
According to ISO standards, the PDF/A format is not compatible with the
PRC format. Therefore, if both modes (PRC and PDF/A support) are switched
on, an error occurs. See Export to PDF using PRC
for details about exporting to a PDF file with PRC support.
Fonts can only be embedded in a PDF/A document and this leads to an
increased document size.