The file, its text and your note, kept together
Every file you attach keeps three things side by side in the project's folder: the original, the text taken from it, and your note about what it is. Write the note in the box under the file, or let AigoPilot take it from the prompt you send the file with. The agent is told all three, and is told exactly what is missing from the text, such as pictures of pages or hidden sheets.