ChatInDoc is an innovative PDF viewer that incorporates ChatGPT, an AI system developed by OpenAI, to provide efficient and time-saving solutions for long and complex PDF documents, such as academic papers, instruction manuals, and IR reports. With ChatInDoc, users can chat with the AI system and ask it to summarize sections of PDFs, explain unfamiliar terms, and analyze IR reports. The AI system is based on GPT-3.5 and GPT-4, which have shown a performance comparable to humans, demonstrating a high level of understanding and capability in natural language processing. ChatInDoc offers a free plan that grants users 2,000 points every month, allowing them to ask around 20 questions. Additionally, it provides a pro plan for $10 per month, granting users 200,000 points every month, which allows them to ask around 2,000 questions. The pro plan also allows users to hold up to 30 PDFs, up to 50MB per file, and to access a more extensive range of features, with no automatic deletion of PDF files.ChatInDoc supports multiple languages and provides a user-friendly chat UI that responds in all major languages. The AI system answers users' questions based on the content of the PDF files, and users need to make their questions specific for the AI to understand them accurately. ChatInDoc allows users to delete PDF files from the server at any time. Overall, ChatInDoc is an efficient and innovative tool that offers users a time-saving solution to analyze complex PDF documents accurately and effortlessly, making AI technology accessible and user-friendly.