◇ Could this help me?
Yes, and the underlying economics are easy to confirm independently. A document sent in its original form carries structure and imagery that are paid for whether or not they matter, and converting to plain markdown first removes that overhead for the very common case where only the words are needed. The free converter named is a real and widely used project, and its tool server version removes the manual step. General practice, with two honest qualifications: the specific saving figure is a marketing number rather than a measurement, and conversion destroys exactly what some documents are for, so anything whose meaning sits in a chart or a layout should keep its original format or be split so only those pages do.
I want to stop paying image-token prices for documents that are really just text. For the kinds of file I describe below, help me decide per document whether its meaning lives in the words or in the layout and visuals. For the text-only ones, show me how to convert them to clean markdown before uploading, and tell me what gets lost in that conversion so I can check nothing important went with it. For the visual ones, show me how to split the file so only the pages that genuinely need their original format stay that way. Before recommending any tool I would have to install, tell me who publishes it, what it does with the files, and what access it needs, and wait for my approval.