Some files are image-only files though (scanned) and would need OCR tools to allow the computer to recognize characters and content.
PDF – Portable Document Format is a lossless file format that is often used in printing and transferring because of its ability to maintain the layout, graphics, and formatting.This is popular with designers and photographers. TIFF – Tag Image File Format is used for image files containing raster graphics.
This is usually opened by using e-readers or software that open eBooks.
In the old days, programs were simpler, fewer formats were available and computers were bigger.