High quality pdf

Hallo, I buy several ebooks from HumbleBundle (DRM free, cheap and you do charity a the same time). They give me both normal/low quality pdf (due to google reading limit of 100mb) and high quality pdf, I download both of them and then import in Calibre, but Calibre imports only one of them (normally the low quality, but I suppose it imports the high quality and then overwrite it with the low quality even if the have different filename). How can I mantain both of them?

Thanks, Pietro.
PS: really a nice software, I supported it a couple of years ago and it worth every penny.