When I search "intel" or "microsoft" in Keyword Planner, it says nothing and display list of keywords ideas with suggested bids etc.
Some competitor websites have copyright to their name and if I want to use such competitor name as my keyword in my AdWords campaign, how can I check if its not prohibited to use in my PPC campaign? (I was under impression that AdWords will show me if particular keyword is trademark and could not be used for PPC campaign)
Depends on country. Each country has different legal regulations on under what conditions brand bidding may or may not be allowed. In addition, each traffic source also has their own rules.
I spoke to chat the other day and they will tell you on chat if its a trademarked keyword. If it is a TM then you need to contact the TM in question and get permission, google supply forms.
Targeted Region: United States
What if I have thousands of brands, chat will not really help.
Usually, if you add the keyword to the live Adwords interface, it won't allow you.