Step 3: Copy and paste these files in LIBRARY folder of Proteus In our example it is ARDUINO.IDX and ARDUINO.LIB You will see two files names as *.IDX and *.LIB in some cases third file is *.HEX. Step 1: Download Proteus library zip file example ARDUINO Proteus library Following are the simple steps to add Library in Proteus Many times we need to simulate different circuits before we actually develop it, This tutorial shows how to add library in Proteus 7 and Proteus 8. Proteus is simulation and PCB designing software.