Q: Can I run Windows 7 on a Surface Pro device?
A: No. The Surface Pro is a class 3 UEFI device, which means it has no Compatibility Support Module (CSM), which emulates the old BIOS environment. Windows 7 is not compatible with UEFI, which means without CSM, it wouldn't be able to function.
If you had to run Windows 7 on a Surface Pro, the only way would be to enable the Hyper-V feature of Windows 8 and run Windows 7 inside a virtual machine (VM). However, this would limit the resources available and the capabilities such as some of the touch/pen features. I would suggest looking at removing whatever obstacle is making the case for using Windows 7.