Someone hacked my Yahoo password...
And change my security questions?
In that I have stored my important documents...
How get I back my password?
Security questions is also changed..
Please help me to get back my password

The ONLY way you may get your account back is by getting in touch with Yahoo and pleading your case.

Hi,
Thank you for posting a question here, and Welcome to the site.
As the other answer stated, your only chance is to contact Yahoo.
Personally, I think you should start another Yahoo account, because the chances of using this one are slim and none.
The chances are that someone already knew your ID and password, maybe from your own computer.
Best of luck.

From someone who uses Yahoo as my primary email account, I can tell you that you are screwed.

I know that's not what you were looking for, but Yahoo Amin won't do anything.

Do you know who hacked your account? Because if you don't, then you are screwed.

Just go create a new account. And I ask you, how did someone hack it?

Did you use accurate information, accurate secret answer? You need to develop better internal security.

For example….always have your birthday one month prior, or one year prior. Some little change only you know about so if someone who knows you tries to crack it, they can't.