To people having trouble registering.
Try this:
Install the software but don’t try to register it.
Drag & drop any pdf into the main window.
Pick one of the conversion types and click on convert.
I used “Source Folder” for the destination only so I could find the files easily.
Do this three more times with different conversion types.
On the fourth conversion, a registration/buy window will pop-up since UniPDF Free will only convert 3 files per day.
Enter the SOS registration information, click “Register”, and you are good to go.
You can select “Cancel” when the window to start the conversion shows up.