Welcome to our community, @Fanny_Marello
I suggest you read these first:
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Binary data: https://docs.n8n.io/courses/level-two/chapter-2/#binary-data
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If you run into file system issues in Docker: https://community.n8n.io/t/n8n-docker-file-system-debug-checklist-2-minute-method/272013/1
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For a beginner-friendly AI agent guide: https://community.n8n.io/t/how-to-build-ai-agents-in-n8n-for-beginners-full-guide-nocode/183469
Especially the AI agent guide around 40:00, because it may help you decide whether reading PDF files from disk is the right approach for your use case.