In a special structure, both as and though can be used after an adjective or an adverb. In this case, they both mean ‘although’.
Strong though he was, he could not beat his opponent.

• Strong as he was, he could not beat his opponent. (= Although he was strong, he could not beat his opponent.)
• Cold though it was, we went out. (= Although it was cold, we went out.)
• Brave though he was, he could not win the duel. (= Although he was brave, he could not win the duel.)
• Intelligent though she was, she could not solve the puzzle. / Intelligent as she was, she could not solve the puzzle. (= Although she was intelligent, she could not solve the puzzle.)

As if and as though

As if and as though mean the same. We can use a past tense after as if / as though to show that a comparison is unreal.

Compare:

He talks as if he knows everything. (Perhaps he knows everything.)

• He talks as if he knew everything. (But he doesn’t.)
• She behaves as if she is rich. (Perhaps she is rich.)
• She behaves as if she was rich. (But she isn’t.)

As if / though and like

In an informal style, like is often used instead of as if / though. This use of like is common in American English. It is not considered correct in a formal style.

• She looks as if she is rich. (Formal)
• She looks like she is rich. (Informal)