"I work as a secretary at an office."
Translation:Ik werk als secretaresse op een kantoor.
When are articles necessary? I put in "ik werk as een secretaris op een kantoor" and got counted off for including "een".
The een before secretaris is optional. However it could be that you were penalised for using secretaris. Secretaris and secretaresse refer to two different functions. Secretaris is an administrative function and can be used for both males and females, secretaresse is a personal assistant and is normally only used for females (for males usually personal assistant, persoonlijke assistent or administratief medewerker is used). See this explanation (in Dutch).
IIRC I was knocked off for the article. I remember triple-checking it because I was befuddled by it, but the article was the one thing underlined in the correction.