Set contextual information just once and then ask questions about it on subsequent queries

I want to create a chatbot using openai-api. I have this large product documentation (700+ pdf pages) and I want my clients to be able to ask questions to the chatbot and receive answers based on this pdf file. If question have nothing to do with this documentation, I want chatbot to just answer “I cannot help you”.

The problem is the size of the document. I’m looking for a way to upload the pdf file to API just once and be sure that all the subsequent questions are answered using this file.

Is this situation possible? Or I have to upload for each query this pdf file as system message?