SimplePDF Copilot is an AI assistant that operates in coordination with a PDF editor. It is capable of performing operations such as filling in fields, answering questions, adding items, and deleting pages. The developer stated that it was designed for privacy-conscious users, such as those in the healthcare sector [Hacker News].
To protect privacy, the PDF files themselves are not transmitted from the browser. All parsing, rendering, and field detection are executed on the client side.
Only the text required by the model and the user's messages are sent to the LLM. While it uses DeepSeek V4 Flash by default, it is also possible to specify external cloud providers by providing an API key, or to operate in a fully local LLM environment using LM Studio [Hacker News].
A key technical feature is the client-side tool calling. The LLM intends the tool call, but the actual execution takes place within the browser. According to the developer, this achieves improved speed and limits the data exposed to the LLM.
Tanstack Start, Vercel's AI SDK, and Tailwind were used for development. A demo version has been released as open-source on GitHub [Hacker News].
Source: Show HN: Filling PDF forms with AI using client-side tool calling（HN 60pt・29コメント）（HN Search (backfill)、2026-05-02）