Select and copy the Chinese text in the pdf, paste it in a new, not yet saved, Notepad document.
Yes, it will display as bars or rectangles, depending on the language in Notebook. But it actually is the Chinese letters, saving the file in UTF-8 (any font) will keep the copy-pasted Chinese letters. Mind though that saving in ANSI or ISO can ruin the pasted utf-8 characters.
But also try the copy-paste direct into the html and save the file as UTF-8, that should work too as far as I can tell.
There are tools that can extract and save text, unformatted, from pdf documents.
The browser should show the Chinese letters, even if the editor maybe can’t like Notepad.
If not, check, as @SamA74 says, that the UTF-8 is used in all steps and also the html meta charset is UTF-8.
Please tell how you succeed, or fail.