The FatFile.h file in the utility folder defines the actual File class. It contains the no-argument read method:
int read() {
uint8_t b;
return read(&b, 1) == 1 ? b : -1;
}
which, as you can see, actually calls the two argument method. So, off to find the two argument method. Well, hey, its the next function:
/** Read data from a file starting at the current position.
*
* \param[out] buf Pointer to the location that will receive the data.
*
* \param[in] nbyte Maximum number of bytes to read.
*
* \return For success read() returns the number of bytes read.
* A value less than \a nbyte, including zero, will be returned
* if end of file is reached.
* If an error occurs, read() returns -1. Possible errors include
* read() called before a file has been opened, corrupt file system
* or an I/O error occurred.
*/
int read(void* buf, size_t nbyte);
Why rely on the documentation when you have the source code?