You Can use viber on Windows by following steps:
1. Let's get the downloading file from the internet, follow this link: Download Viber for Windows
2. After finishing downloading the file, which is very small-sized, open it and click "Accept & Install".
3. You just have to wait, it may take a long time if you have a bad internet reception.
4. Now it will ask you whether you have a working Viber version on your smartphone, just choose yes.
5. Then enter your country international code and your mobile phone number (which you used to access Viber on your smartphone).
6. Now, Viber will automatically send you an activation code to your phone, just enter the code in the space, check "I have read and accept the Viber user license agreement". At last click on "Enter Viber"
7. Congratulations, now you have Viber on your PC!