I Would like to promote my website in many countries for that I would register domains using the correct extensions for each country. For example if I am targeting France use .fr and for Uk use .uk or will using a .com be OK?
The .com is a business extension and the first and most widely used you can be in anywhere in the world and register it with no problems.
.com means commercial, its based for all over the world.
.com is universal, but I think registering as many of the extensions as you can is also a smart move, as whatever they do search in, you'd have them covered
The .com is a good choice and easier to remember.
some people have wrong idea, that .com domains were created for american usage.. this myth has been proven wrong by the fact that the .us extension has been created. Most of the domains that I own are .com, and it is the largest and seemingly most popular domain extension.
If it's available in .com then you should get it, and try and get as many extensions as possible because you don't want another company snapping it up before you manage to get it for your company..