"It is hard to read a thick book."
BIG BAD BUG: I tried writing atsui with kanji and without kanji, and the only accepted version has both hiragana and kanji, like this: あつい厚い本を読むのは難しいです
Just had the same one. あつい厚い is the same word twice... if it tries to signal me to use the version written in the right kanji, it does a terrible job at it.
I know I am having trouble with this (at least, with respect to Duo), but I really think the topic and object markers are backwards. Seems like "Speaking of thick books, it is hard to read them." makes a lot more sense than "Speaking of reading, thick books are hard." Still hoping to find that secret decoder ring that helps me figure out which is which.
It's hard to know which "atsui" is used here. Of course you'll understand by the context, but maybe introducing the kanji would be better.
While reading a high temperature book would be difficult I think one could safely assume that that isn't what the sentence is referring to.