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As you have found the downside of PDF can be that you end up with a large file size, which can be slow on a tablet. You may want to scan the words and the maps separately - keeping the maps at a high resolution, so that you can see lots of detail. But for the text either scan at a lower resolution, or use some OCR (optical character recognition) software to convert the scanned image into text, which will be much smaller in file size - although you are likely to loose the formatting and fonts etc of the original.
...years ago I used one called pdf sam, no idea if it is available for MAC or if it is still any good at all...