TeX will insert
\endlinechar at the end of line.
If the value of
\endlinecharis negative or greater than 255, no character is appended, and the effect is as if every line ends with %.
Even if the
\endlinechar has been changed to greater than 255, the character is still append to the end of the line, which cause the effect as
\par at the end of the line. What is the reason?