So, I don't think that the first two parts, converting the PDF page to an image to get the text, is necessary. One could just use the basic information in a PDF content stream to get the bounding box for each character. The resulting information can then still be analyzed using the layout analysis algorithm mentioned as step 3.

The information would also be more exact since extracting the character positions from an image depends on the rendering of the PDF to the image (i.e. if an A4 page is rendered at 300ppi or at 600ppi or higher).