Regarding “document formats”
You first need to define some basic requirements, primarily whether the document should be editable or not, and another might be whether a special application viewer might be required for simply viewing.
If editing is not an issue, then documents which display individual text characters can be considered, and then quality will depend on the quality of your font library and how well the viewer app renders the document. Because you have no consistent control how well the document will render, this is often not a preferred choice for document creators.
If the document is not to be edited and as a document creator you want to have reasonable control over quality no matter on what device the documented is viewed, then an image-based format is generally preferred, with all its ramifications.
If you know graphics, you’d know that there are two main ways to define a picture, either by each and every individual pixel(ie raster, or bitmap) or by vector(shapes defined by algorithms).
Rasterized images can maintain high quality at a very wide range of display sizes by simply removing pixels as needed and although not desirable through extrapolation. One major drawback of rasterized images is that if you want to maintain extraordinarily high quality for very large images, the number of mapped bits is very large so the file is very large.
Vector based images are also very popular for their ability to display images with very small files, compared to rasterization. By defining common and recurring shapes with an algorithm, you can also often get shapes with smoother edges by use of dithering which although might be possible by rasterization would require even more data. If you consider a web page as a kind of document, all web pages display their content through vector based graphics.
A PDF is actually an image format, so based on your personal experience you should be able to guess which type of image format a PDF is… (of course, it’s rasterization). The file size is enormous only because you want such fine detail <at an enormous viewing size>. If the file will be seen only on mobile devices, you should re-compile(convert) the PDF to the viewing size, eg 320 pixels on a 3x5 inch screen. The result would be a file that looks fine on that size screen but lousy on a big monitor, at a reasonable file size.
You can also do a search on vector-based document formats and experiment with those, but as I described above you’ll need a special viewer for that format so make sure the viewer is available first.
There’s plenty more than the generalizations I just described, you can either read up or just do a lot of experimenting which I suspect you’d need to do anyway.