I want to select a pdf file from the bot and send it through a Web Api but I have not obtained any documentation, if you could support me with this it would be very helpful.
Thank you.
You can send a PDF, but you cannot send a local fie. It has to be uploaded somewhere or encoded. So, sending with activity and contentUrl of either data:image/png;base64,${imageBase64} or https://www.example.com/path/to/file.pdf
Please see more info explained in this comment. Also be aware that different channels behave differently with attachments (See end of conversation in that same thread).
Edit: Actually, the change to be able to send a binary is currently in the works. Please watch here.