The QCAD Demo and the QCAD Pro version are two different programs (i.e. it is not the same program that can be switched from Demo to Pro mode and back).
After purchasing the Pro version, you must download, install and use the Pro version instead of the Demo version. I guess that you either have the Demo and the Pro version installed side by side and you are now starting the wrong version or that you have only been using the Demo version so far and you never downloaded and installed the Pro version at all. To do this, please proceed as follows:
Visit our online store at:
-> Click "My Account"
-> View appropriate order
-> Click "download" button beside appropriate product
-> Download QCAD Professional for your system