What do you read, my lord?
Words, words, words.
A really good reader reaches a stage where he or she does not see the words but sees, hears, and senses the things the words represent. Once a person has achieved that ability, he or she is able to travel freely in what Keats called "the realms of gold." A good reader can travel anywhere in time or space.
Hamlet is undoubtedly a good and voracious reader. He is able to read in many different languages. Still, even the best reader can have a problem if he or she is seriously ill, troubled by a serious practical matter, or feels extremely depressed, frightened, or angry. Sometimes the words on the printed page become just so many little black marks that refuse to yield the images they are supposed to represent. Perhaps this is what Hamlet means when he tells Polonius he is only reading "words, words, words."
We have all had that experience of trying to escape into a book and finding the words are as opaque as if they were in a language we don't understand. Hamlet is reading words but not getting anything out of his reading because he is so seriously troubled by his practical problems and also so seriously depressed.