The file is not a binary file, it is just a plain text file using UTF-16 big endian encoding (most text files are ANSI). To read/write it, you cannot use open/read-line/write-line on AutoCAD, as these do not support Unicode double-byte encoding.
Instead, you can use the ADO Stream object - here are some existing examples from VovKa:
https://www.theswamp.org/index.php?topic=39617.0