Dear Sir/Madam,

Thank you for your letter [date]. I'm glad you're going to [the place] next month. I'm glad to see you at the [exhibition/fair].

Our company will hold a reception in [hotel] on the evening of [date], and I will be very happy if you can attend.

I look forward to hearing from you as soon as possible.

You are sincere,

[Name]

The following contents are for reference: Baidu Encyclopedia-Invitation Letter