It’s not that far-fetched, PDFs in my opinion are closer to vector graphics than to document formats like odt and docx. They have no understanding of format if not using advanced features, like a table in a PDF is just spaced text with lines between them, and text is just independently placed letters. In fact the space symbol doesn’t exist in most PDFs, it’s just that two letters were spaced further apart. So they basically are multiple canvases that are being painted on with letters, lines, fill areas and even bitmap graphics.

Modern PDF actually does further in the direction of a document format by providing the content in a structured way, mostly for accessibility, but also for making the format suitable for automatic processing the contained data.