You can load new files into memory at anytime. These can be appended to a current file, replace a file, or be loaded into a new buffer (for details on the later, see Chapter 8.1.5).
The [Esc][`] command (also accessible as Menu-File-NewFile) first saves the current buffer. Then a prompt is displayed to load a new file into that buffer. The existing buffer data (hopefully saved at this point) will be destroyed when the new data is loaded.
If you press [Enter], without entering any data, the on-screen file selector will be enabled for you to select a filename.
The command will prompt for a filename (press [Enter] with no data to enable the on-screen file selector). The specified file will be loaded into the buffer at the current cursor position. The filename associated with this buffer will not be changed.