vdx to pptx conversion is referring to the usage of MS Visio drawings assets in Microsoft PowerPoint, using the drawing as object on one of the slides. You can actually do this with PowerPoint or any other similar tool, such as SmartDraw.
Some online converters advertise this conversion as well, but the results of these are often questionable - in this case the result would be empty presentation with just the drawings imported or something similar.
Updated: September 18, 2023