I wish to open a sales office in this state, but I do not want it headquartered here. how do I open the office in another state?

As long as you have a registered agent here, you can have a headquarters anywhere. The idea is you need a street address where process can be served in Washington. Good Luck

Microsoft, for example, has most of its employees and workforce in the Seattle area. However, Microsoft is not a WA corporation. Many other corporations and other business entities are not WA entities.

You will need to check the laws of the state in which you want to be incorporated and headquartered.

One general requirement likely is that your business has an in-state physical address with a physical person at the address to accept legal documents. In general, there are businesses whose business is to accept legal documents for other businesses.

Businesses that are formed in other states must be registered with the State of WA to do business in WA. Your business will be subject to the taxes, licenses, and permits that similar businesses in WA must pay.

Besides WA laws, your business will be subject to the laws and taxes of the state in which it is legally formed.

You may want to review your specific facts with your attorney. Among the issues likely should be whether it is good for your business to be subject to the laws of both WA and another state.

There are two answers to your question: If your business in Washington is sporadic, you might be able to avoid registering in the state. If your presence is going to be regular, then you probably have to register as a "foreign" company (foreign to this state) and secure a registered agent. That process is simple. If you are in a regulated industry you may have to register with the division that registers your industry. It really is best if you secure a consulation with a business lawyer who can guide your next steps. You need legal advice to determine if you should or should not register.