[OmarShehata]

There's a lot of good advice in here about how to work around this situation but the best thing you can do here could just be: email this company and ask them.

If you are paying for this proprietary software, especially if you're still in the "evaluating whether we should spend a lot of money on this" phase, you should absolutely push back on them. Ask them all the questions you need, big or small. It's really on them to give you something well documented, and if they don't, they better be willing to answer all your questions about it.

I've seen this sort of customer behavior be the catalyst to get companies to actually document their stuff because all their engineers time was spent answering the same questions over and over.