MPLAB X have the possibility to store source code files in several different character representations.
When the MPLAB X project is created, or a new source file is created, it is possible to select the character representation to be used. Possibilities may be plain 8 bit ASCII characters ( one byte per character),
UTF-8 Unicode with variable number of bytes for each character, or UTF-16 Unicode with 2 or 4 bytes for each character.
MPLAB X will know what character representation was used in the file when it was saved.
MSWord is not suitable to edit software source code files, it is likely to insert formatting codes, and / or change character representation, in ways that will destroy the contents as software source code.
Microsoft Notepad may be used for simple edting purposes, usually without making problems.
There are other cross-platform editors that may be used for source code editing:
Notepad++ or UltraEdit may be used, and may convert between different character representations,
there are many other possibilities: https://en.wikipedia.org/wiki/List_of_text_editors
Also the editor in Microsoft Visual Studio, may be used to edit source code for MPLAB X source files,
if it is installed.