How can I address inaccurate responses from Assistants?

I’m building a simple chatbot using the Assistants API and have attached a PDF file containing specific information as a retrieval tool. However, when conversing with the final chatbot, sometimes it provides correct answers, but other times it gives inaccurate responses or general answers (not based on the PDF file). How can I resolve these issues?

For reference, the PDF document is written in the legal framework of South Korea. Could it be confusing for the chatbot since it’s not in English but in Korean?

Please ensure that the correct description and instructions have been included as per the guidelines of your assistant.