my computer is from 2011 i can't install his old system tell me that this file is missing

Yes. This is from an apple document:

macOS Sierra 10.12 can upgrade El Capitan, Yosemite, Mavericks, Mountain Lion, or Lion

Since you're running Snow Leopard you'll have to upgrade to Lion first and then use this link to upgrade to High Sierra: macOS High Sierra 10.13

Since Lion is only available thru purchase you'll need to shell out some $$ for it.

FWIW that model iMac is considered vintage by Apple.

I am very sorry, but you have provided us with no useful information to respond to. Your comment makes no sense. Please read the information on the link below and then respond with some specifics we can respond to. Thank you.

Writing an Effective Apple Support Communities Question - Apple Community

Hello, did you read the post that explains what we need. Again it is Writing an effective Apple Support Communities Question , please re-read and then re-write your question so it has some context. We cannot read your mind or look over your shoulder so we need your help by including some context in your question. The way it reads now is like asking a total stranger, "My house is not working right, what do I do to fix it?"

High Sierra is 10.13.x, not 10.6.x.

You need to download and pay for Lion 10.7.x first from https://www.apple.com/shop/product/D6106Z/A/os-x-lion

Once you have downloaded and installed Lion, then backup the computer!!! This is critical to safeguard your data. Then use the Mac App Store to download High Sierra 10.13.6 the most recent version of Mac OS for a 2011 iMac. I would STRONGLY recommend your computer have a bare minimum of 8GB of RAM, however 16GB is better. Current versions of Mac OS use more RAM than Snow Leopard. If you do buy RAM then please only purchase from Crucial.com or Macsales.com.

Good luck.

Again, an incomplete post so you are making it difficult for us to understand. We need a question that explains your problem, for example, "I have a 2011 27" iMac that has 4GB of RAM and it is currently running Snow Leopard, version 10.6.3 and I want update it to High Sierra 10.13.x. What steps do I need to take to do that?"

Once again (and for the last time) you did not explain this, again I am not a mind reader. Yes, you must buy 10.7.x, it is the last paid for version of Mac OS. You indicated you have 10.6.x. installed and want to upgrade to High Sierra (10.13.x), in order to do that you FIRST must buy 10.7 for $19.99 and then after you have 10.7.x installed that you can download and install High Sierra at no additional cost. You cannot jump directly from 10.6.x to High Sierra 10.13.x.

You'll have to borrow a computer, go to the Mac site and purchase Lion. You might check with the local Apple store or Authorized Apple Service Provider  to see if they have the discs in stock so you can pick one up quicker.

Put the CD in the optical drive and start the computer with the "C" key held down so as to boot from the CD.