HTML files can be opened with pretty much every text editor, so there is no need to convert them. Should you need it, you can simply rename the HTML extension to TXT. Alternatively, you could view the HTML file using any web browser and copy paste the text to a text editor. If you want to get rid of the various HTML tags, use the "paste as plain text" function instead simple paste.
Professional HTML editors are probably the best software for this. You can find more options in the html to txt conversion entry.Open HTM file Open TEXT file
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