PDF Specification
The PDF Specification describes the required electronic format. The specifications are required versions of the PDF standard and must be followed in order for the data file to be processed. You can choose the specification from 1.3 to 1.7. It’s recommended to keep the default setting (auto) if it’s not entirely clear what the PDF Specification is.
To configure specification, go to Tools > Settings > General from the main menu:
It is also possible to convert the file to PDF/A format. To do it, go to File > Export > Convert to PDF/A from the main menu or use the keyboard shortcut Ctrl+Shift+A.