I downloaded AN4370SW today and tried to install the driver on my Windows 7 machine and I was able to install both DFU Runtime and DFU Device drivers. Did you follow AN4370 section 5.4.1 Driver installation, especially the "Have disk..." approach ? This worked for me. Windows 7 complain that drivers are not digitally signed, so I used force option to install them and then they worked.
I use twrk70f120m with TWR-SER.
First I load the DFU bootloader application for K70 into the board using CW 10.2.
Then I restart the board with the SW2 button on processor board pressed; then I plug-in usb cable into my PC. Windows 7 then install USB HID device automatically, and I use "Have disk..." to force intallation of DFU Runtime.inf.
Then I unplug the usb cable and plug it back and use "Have disk..." to force installation of DFU Device.inf.