Several possible dst to pdf conversion exist and all of them deal with export of some graphics to PDF format. The most common need to covert dst to pdf would be when someone tries to export Tajima embroidery design (.dst) as PDF for preview or printing purposes.
Another conversion is related to AutoCAD, which uses .dst files as some sort of sheet sets. Unfortunately, we couldn't really found anything specific about this particular dst to pdf conversion.
Updated: January 17, 2017