What is the most frustrating part of preparing documents for AI?

I am building Claupt, a set of browser-based tools for preparing material before it goes to an AI model. I would like to learn from people who do this work regularly.

When you work with PDFs, copied web pages, code, or JSON, what takes the most time before you can get a useful result from an AI assistant?

Is it cleaning layout noise, fitting the context window, splitting content, preserving structure, checking sensitive information, or something else?

Specific examples would help us prioritize the next improvement.