I have lighoom 5 on disk but have just bought a Mac computer and have an ipad. Can i put Lightroom on to them without a disk drive?

you can put it on your mac, but not on an ipad.

for your mac:

Downloads available:

• Suites and Programs:  CC 2014 | CC | CS6 | CS5.5 | CS5 | CS4 | CS3
• Acrobat:  XI, X | 9,8 | 9 standard
• Premiere Elements:  12 | 11, 10 | 9, 8, 7
• Photoshop Elements:  12 | 11, 10 | 9,8,7
• Lightroom:  5.6| 5 | 4 | 3
• Captivate:  8 | 7 | 6 | 5
• Contribute:  CS5 | CS4, CS3

Download and installation help for Adobe links

Download and installation help for Prodesigntools links are listed on most linked pages.  They are critical; especially steps 1, 2 and 3.  If you click a link that does not have those steps listed, open a second window using the Lightroom 3 link to see those 'Important Instructions'.