After purchasing ZAD theme please navigate to your downloads tab on Themeforest and find ZAD Theme. Click the download button next to ZAD theme and choose All Files and document choice, save the package on your computer.
Please unzip the downloaded ZIP File . Inside the extracted folder, you will find Folders like Documentaion , Licencse and Upload. Inside upload you can find your main Theme Folder (ZAD) and the child Theme folder (ZAD Child)