Why PDFs don't actually contain tables
A PDF page is a stream of drawing instructions: place this glyph at this x/y position, draw this line from here to there. There is no native "table" object in the file format — the visual grid you see is an illusion assembled from text placement and ruled lines. That's why any tool relying on those visual cues (ruled-line position, column alignment) is fundamentally reconstructing an illusion, and inherits every edge case where the illusion breaks: unruled columns, cells that wrap to two lines, headers repeated on every page. Semantic extraction sidesteps this by asking a model "what does this data mean," not "where do the lines fall."