Adobe Air.......to quote " Adobe Integrated Runtime (AIR) is a cross-platform runtime environment for building rich Internet applications using Adobe Flash, Adobe Flex, HTML, or Ajax, that can be deployed as a desktop application."
Now do you really want that, unkyUb.....probably not.
I notice too that to download Adobe Air as a standalone it is a 15.11mbs file.......add that to the 26mbs odd for Reader and you come close to the 43mbs odd that you see.
That will explain the difference......direct from Filehippo...Reader only, from Adobe...inclusive of Air. ( And I seem to recall that as Air is a cross platform app. it will install bits of Apple software in the way of "Bonjour Service".
Maybe you could consider uninstalling your Reader, Air and associated bits and getting a clean, smaller download from Filehippo and rinstalling..