The empty zip file may be due to your proxy server settings - I have the same issue, which is why I need to use HTTPS for download.
The reason why you're getting a PDF file is because you're downloading instructions...
Have another look at the information in the Customer Center:
TRADOS 7 Freelance
For instructions on installing TRADOS 7 Freelance and the softkey license, download the below documentation applicable to you:
* Installing TRADOS 7 Freelance as New License, if you are not yet using TRADOS Freelance
* Installing TRADOS 7 Freelance as Upgrade, if you are an existing TRADOS Freelance customer
* Installing TRADOS 7 Freelance for Early Bird Customers, if you purchased your new license or upgrade during our Early Bird campaign
Additional and localized documentation on using TRADOS 7 Freelance is included in the TRADOS 7 Freelance Installer.
You will need to download the installer to get the installation file, plus additional documentation.