I have Lightroom 5 on a CD which I loaded on my imac. I now intend to buy a Macbook Air, which doesn't have an optical drive. Will it be possible to load the programme online using the serial number on my CD.
Yes. Just download the trial version and install it. Then use your serial number to activate the trial version and it will be the full version of Lightroom. Actually, the trial version is the full version. It just as a time limit programmed into it.