The font used for text is Computer Modern/Latin Modern. However, the third sentence is actually a feature of the mathematical environment. General variables in the mathematical environment are written in italics, while numbers or symbols are written in block letters. In general, this is not done in the text. Ignore letters or numbers in the text and use italics in the text. If it must be changed, it is not recommended and should not be changed. You should package all the western languages in a mathematical environment, either black a font, black a font yourself, or better black a virtual font macro package, but I think the topic is mainly at this level, so I probably won't ask. The main reason why there is no way is that the fontspec package we generally use to control fonts does not provide the function of replacing fonts within a certain Unicode range. I only played this function in ConTeXt Mark IV, which is similar to \ setmainfontfallback [Arial Unicode]? [range = 0x3400-0x2fa1f] \ setmainfontfallback [times new Roman] [range = Cyrillic] controls a certain range of things. For details, you can see the simple fonts material of context-simple fonts-context wiki, which was used to deal with multilingual issues at that time. At first, I used a simple font module, but later it seems to be directly integrated into the engine (the game of context). However, due to too few people and insufficient information, I haven't played much since, but it is more than enough to set fonts for numbers and letters respectively. The ConTeXt in the impression, as well as the fonttable that can be a variety of hackers, is also a variety of pits. I suspect that it may be more convenient to do these things in LuaTeX. After all, ConTeXt Mark IV is the engine made by LuaTeX. ApTeX seems to provide a relatively open VF mechanism, and it seems much more convenient to do these things in that case. To change the mathematical font of the built-in formula, the font must support Opentype Math. Important: Although Word supports changing these fonts, Office itself is limited. The built-in pdf output only supports Cambria Math to convert into vector text, and does not support other mathematical font conversion formulas to convert into vector text. But the forced conversion to bitmap causes the fuzzy plug-in PDFMaker to be embedded in the mathematical font set.