AxCrypt does not support pre-boot encryption. AxCrypt is a file encryption software, not a disk encryption software.
AxCrypt is only limited by available hard disk space. If you have enough space, then you can encrypt the full drive. But based on the system configuration AxCrypt will work as much as faster
Encrypting folders and files required to boot or run your operating system or any other program is highly discouraged and can prevent access to your OS or programs. Do not activate recursive encryption when encrypting folders and/or files on “C:” drive.
Because AxCrypt application also is installed in your OS(C) drive only. But you can encrypt folders(other than system files) inside the C drive.