When reading an e-book on a mobile phone, it said that the file exceeded 5M. It might be because the size of the e-book file exceeded the storage capacity of the mobile phone and could not be stored. Under normal circumstances, the phone would compress the e-book file by default to reduce the storage capacity. If the e-book file exceeded the phone's storage capacity, the phone might prompt that the file was too large and needed to be compressed again. In addition, you can also change the file size by changing the file name to a smaller number or letter to reduce the file size. If you still can't solve the problem, you can try to copy the e-book file to another storage device or try to compress the e-book file again.