Click 'Version' in the 'Class List' on the top left of the IDF editor and then click 'New Obj' from the tool bar on the top.
'Obj1' will appear in the first line of the bottom window.
Write '2.0' in the 'Version Identifier' Field of 'Obj1' as shown in the figure below:
Information from the EnergyPlus Input Output Reference: "The Version object allows you to enter the proper version that your IDF was created for. This is checked against the current version of EnergyPlus and a Severe error issued (nonterminating) if it does not match the current version string."
Save your file: You can save your file with any name. In this tutorial the file is names as 'tutorial.idf'. Keep saving your work frequently as IDF editor does not save file automatically.