Hi
I intend to buy Avast Pro for 1 year.
If I Use The License in my PC, and after a month (for ex.) format the PC, i can use the license again. Its right?
I know its a stupid question, but i want to confirm. 
yes
The license is a file that must be downloaded and saved to your HDD or SSD.
You then need to insert it in the appropriate place during the install of avast! Pro.
If you reformat your HDD make sure that you have saved the license file someplace else before reformatting the HDD so that you will have the license file available to insert during the installation of avast! Pro on the reformatted HDD.
Thanks for all