This is the tax registration issued by the district tax office where your company located physically, and need to register a proper business scope as well as the biz address.
You need to check the validity of the Tax ID when you issue a tax invoice to your clients or receive one from your suppliers, some times they issue it manually to charge you 10% VAT with a Tax ID which is not valid anymore.
The Registration No.(사업자등록번호: 123-45-67890) should be 10 digit without exception and will not be changed even if your company's name, address, the name of representative director or shareholders' was changed if it's a corporation.
You need to keep the original copy of this registrar carefully, since a lot of concerned parties (especially Immigration office, Banks) will ask you to show the original copy while submitting copy one.
You can change or add a biz scope if it's already on the purpose of business at your "Company Registrar(법인등기부등본)", otherwise you need to add a business purpose at the company registrar first and can add it at the tax office.
You can't issue a tax invoice without this registrar, it means you're not a sole-proprietor or corporation, so don't need to file the VAT Return. Actually you can file the VAT return with this registrar to get VAT refund as well.