Custom GPT doesn't read uploaded books (.docx files)

When I create a custom GPT there is a possibility to upload files.
When I upload a book (700 pages) in .docx format
And I ask chatbot to get some information from this book
Then it says that there is no such info
But it actually is here

My question is: is there any file length limit for using it as a knowledge base?
Is it possible to create a custom GPT but with some books uploaded that then will consult based on these books?