I'll just throw this out here in no particular order:
A guide for installing the CLI (that has become sort of the standard): it has worked for me and many others, and should include the openSSL you're looking for.
It could be that it's installed but not in your PATH. You should be able to access that through the control panel -> system -> advanced system settings -> environment variables. Better yet, Google for it, since there are ton of guides out there already that can explain the process better than I ever will.
As for the .der file, it downloaded just fine for me (Opera, windows 10). I've zipped it up for you, and you should be able to download it [here][1] (at the time of writing)
That's hard to do because there are so many different configurations of hard/software out there, that makes it almost impossible to create a tutorial for everything. There's a (community made) installer for windows for most of the software:
That's to keep it modular so it's applicable to multiple setups, rather than writing new tutorials for every possible configuration out there. At least, that's what I like to make of it.
Give some of the above a try, and let us know if you need further assistance.
[1]: http://jordymoors.nl/particle/cloud_public.zip