implement partial save for large documents to save flash wear
In case of textbooks a person is likely to read 1 or 2 chapters, at a sitting. for example I am reading a textbook with 400 chapters with a total size of over 700 MB.I'm never going to read more than 2 chapters. maybe 1 MB. Writing 700 MB to my sd card,several times a day, will quickly wear it out--specially as micro SD card are TLC NAND.