As it says on its website, Pandoc is a “swiss-army knife” for converting files from one markup format into another.
Recently I had to help someone who had created an extremely complex document in Microsoft Word that needed to be converted to LaTeX. After tinkering with some settings, Pandoc created a LaTeX version that required only minimal editing. The entire process of the conversion took less than an hour, from installation to final edits.
It is not a tool I use very often, but when I do I am always thankful Pandoc exists.