请问下面这个句子有错吗？谢谢

it 作形式主语是固定的用法。

错在‘for’后面不应当跟动词不定式。
1. That's/It's hard for somebody to do that.
2. That's/It's for doing that.

错了。
多了个for。
照猜应该是说“那个很难做”，那就应该是“That's hard to do."

It is hard for sb to do sth . It是形式主语

It's hard to do that.

or

It's hard for him to do that.