IDFVersionUpdater can convert multiple files at once using *.lst .lst file. Refer to AuxiliaryPrograms.pdf and search for section IDF Version Converter / Transition File Lists. If v8.4 v8.4 files a.idf, b.idf a.idf, b.idf and c.idf c.idf are in folder C:\EnergyPlusV8-8-0\PreProcess\IDFVersionUpdater, C:\EnergyPlusV8-8-0\PreProcessIDFVersionUpdater, then 84to87.lst 84to87.lst file should have the following contents

contents
a.idf
b.idf
c.idf

Then IDFVersionUpdater IDFVersionUpdater should choose Files of type type as Text File With List Of EnergyPlus Files (*.lst) (.lst) and select 84to87.lst. 84to87.lst. check Create Intermediate Version Files Files if you want to save intermediate versions 8.5, 8.6 etc.This way IDFVersionUpdater should be run only once and there is no need to run various Transition-Vx-1-0-to-Vx-2-0.exeetc.etc

IDFVersionUpdater can convert multiple files at once using .lst *.lst file. Refer to AuxiliaryPrograms.pdf and search for section IDF Version Converter / Transition File Lists. If v8.4 files a.idf, b.idf and c.idf are in folder C:\EnergyPlusV8-8-0\PreProcessIDFVersionUpdater, then 84to87.lst file should have the following contents a.idf b.idf c.idf Then IDFVersionUpdater should choose Files of type as Text File With List Of EnergyPlus Files (.lst) and select 84to87.lst. check Create Intermediate Version Files if you want to save intermediate versions 8.5, 8.6 etc.