From the documentation you refer to, the remote directory where you will upload the file must be an Oracle directory.
- create directory on the remote database
SQL> CREATE OR REPLACE public DIRECTORY MY_DOCS as 'C:\FTP\files';
- then only you will be able to use it as intended:
ftp.get( p_conn => l_conn, p_from_file => 'C:\oraclexe\app\oracle\files\file.pdf', p_to_dir => 'MY_DOCS', p_to_file => 'file.pdf');