If you need to save your AutoCAD, Inventor, or Revit drawing to the ISO format for long-term archiving - PDF/A-1b, you can use the following steps.
The Adobe Acrobat software installation (e.g. version 8) installs also the Acrobat Distiller application and the "Acrobat Distiller" (or "Adobe PDF") virtual printer. You can use this printer driver to print from any Windows application.
First run Distiller and switch to the preset mode "PDF/A-1b 2005 (RGB)" (or similar, or set the "PDF/A" compatibility for your own mode).
Inside AutoCAD you can setup this mode through "Custom properties" by the "Adobe PDF" printer.
Then in your application (e.g. AutoCAD) perform a standard print to the "printer" Acrobat Distiller (or Adobe PDF). After the print finishes, Distiller automatically converts the print file to the resulting archive file in the PDF/A format.
Alternatively, you can also use the PDFCreator and select (Printer > Settings) the format "PDF/A-1b".
The option "PDF/A-1a" (i.e. incl. the document structure) is not available in these workflows.