Rather than downloading files from here, you are strongly advised to type the command
net from http://personalpages.manchester.ac.uk/staff/mark.lunt
into stata and download from there. This ensures that the correct files are downloaded to the correct places.
optmatch.WIN:(This file is for the WIN platform, and should be renamed optmatch.plugin for use)
optmatch.LINUX:(This file is for the LINUX platform, and should be renamed optmatch.plugin for use)
optmatch.WIN64A:(This file is for the WIN64A platform, and should be renamed optmatch.plugin for use)
optmatch.LINUX64:(This file is for the LINUX64 platform, and should be renamed optmatch.plugin for use)