If you buy some new software and it has a product-activation code, e.g. for 25 characters long, write it down in a .txt. file, labelled clearly ‘programme name activation code do not wipe’/
I wish I’d done that when I installed my version of word about four years ago. Thought I could solve problems by reinstalling it and couldn’t, so am now the proud owner of ‘MS Office Home and Student version 2007. Ho hum.