Linear Voltage Reduction Device
Here is a possible way to do this. Note that it cannot supply negative voltage, so Vout = Vin - 5.0V), and current should be more than 1mA so there has to be a relatively low load resistance at low output voltage. If you do not draw at least 1mA+ the output voltage will rise. R4 below is the output load. 





Here U1 is a TL431 shunt reference. The transistor will be okay up to an ampere or two with proper heat sinking.

Edit: Vdrop = 2.495V * (1+R1/R2) so by changing R1 the drop can be changed to whatever is required from about 2.5V to about 30V. The graph shown is for 5V drop. If you change R1 to 18K you'll get about 7V as @Jasen comments below. It still will be fine from 1mA to 1A with proper heat sinking on the TIP32. 

A simple 1W zener will work too- but you cannot be adjusted and won't be as stable or accurate. 

Here is an example for comparison (using a 7.2V nominal SMT 1W zener): 



And, finally, and in order of poorer performance, a string of 10 1N4148 diodes: