NotebookLM is the strongest fit here because it is built specifically for ingesting long documents and generating grounded summaries, and it is free with a Google account. You upload the 50-page document directly, then ask it to produce a brief summary or a set of key points, and it stays anchored to your source material rather than hallucinating. Claude Sonnet is a strong alternative when you want more control over summary length and tone through a conversational prompt. Gemini Flash works well if you want a free, fast option via the API or the Gemini app with a large context window.