An XeLaTeX Compilation Error: Undefined control sequence. \pdfglyphtounicode

Today, when I compile a .tex file (which I created on another computer before) in TeXstudio, some errors like Undefined control sequence. \pdfglyphtounicode are printed in Log box:

But on the other hand, corresponding PDF file can be normally generated, and I can preview it as usual. Besides, these errors don’t exist when I compile other .tex files.

Later, I notice messages in Messages box:

which shows that complier pdflatex works well but xelatex doesn’t. Probably this is why above case appears.

I remember that previously these two “green” lines always appeared after a successful compilation, and I thought they indicate that everything is OK, so I have never read it carefully. Now I realize that I have been using two compilers to compile .tex files all along, and Default Compiler configuration also shows this point:

After I changing Default Compiler option from txs:///pdflatex | txs:///xelatex to txs:///pdflatex, that is cancel xelatex compilation, aforementioned errors disappear. So, I guess these errors are caused by that some characters in this .tex file are not supported by xelatex (but I’m not certain, because all characters in the file are English letters).

As introduced on 31th page of Prof. Liu’s book, Introduction to LaTeX¹, there are different compilation methods, and hence different compilers like pdflatex², xelatex³, and dvips⁴, to convert TeX source code to PDF file, and in which xelatex can best support processing Chinese characters:

So, I think for this reason I added xelatex as a default compiler before.

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