I'm writing about certain historical leaders of China, and I'd like to say something along the lines of "he opened China to foreign investment" or "he opened China to foreign influence", etc. I can translate it except for the "opened", part. I know 开 means to literally open something, like a door, and I've put my sentence into various online translators and gotten "开放" for "open" in context. Does that work or should I use something else?
Sounds right. Something along the line 对外资开放, which means give access to foreign investments.
Or you can say in the literal sense, that 他打开了中国的大门。or 他向外商投资打开了中国的大门。
to check that 开放 works find example phrases at online dictionaries, e.g. iciba, bkrs, submitting e.g. "opening to outside" get 对外开放 [法]open door to the outside world； [法]open to the outside world； [法]opening to the outside world + many more examples, also note Chinese motto (邓小平)改革开放 find many more examples for 开放 at bkrs