Spellchecker marks misspelled words in red in one go but when I save the document in any format or copy those underlined words to other programs these red squiggly lines always disappear. How do you save them permanently so that they will be visible when printed?

You could take a screen shot of the page and then print it. Alternatively, apply some other formatting that will actually print, such as a different text color. The screen shot is probably easier, assuming that there aren't too many pages in the document.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional