Not sure I understand.
What is the file, and what do you want the bot to do with it?
In general you can add a link to a bot's message to link a file.
You can upload the file to any file hosting service such as Drop Box to get a link for it. The bot's also have there own file repository you can create a link in if you wish. But basically you need to upload the file somewhere and return the link to it in the bot's message.