opened its doors

[keannu]

Why is it a plural form "doors", when "open its door" seems enough?
Does it mean "start a business" or "open/provide information to the public"?

pr88
ex)The first African-American director was William Foster, whose Foster Photoplay Company opened its doors in Chicago in 1910...

 

[Chicken Sandwich]

5start operating [ intransitive and transitive ] ( also open up ) if a place such as an office, shop, restaurant etc opens or is opened, it starts operating or providing a service : Sarah had recently opened an office in Genoa.
French and Scandinavian offices are due to open in the autumn.
The Forestry Commission has opened a plant centre selling rare plants.
The centre has been a great success since it opened its doors a year ago.

Source: Longman Dictionary of Contemporary English

 

[SoothingDave]

It's idiomatic. Many businesses have more than one entry place, or at the very least double doors at the one entrance.