If you want to do single-file conversions with Pandoc without having to install it, try http://markup.rocks/. It’s a compilation of Pandoc into 2.2MB of JavaScript so you can convert documents (and preview their HTML conversion) in your browser as you type. Its source code: https://github.com/osener/markup.rocks.
I most often use http://markup.rocks/ for converting HTML to Markdown and for testing that my reStructuredText syntax is correct when contributing to docs.
Pandoc also has a demo web page for trying it out (https://pandoc.org/try/). The demo supports all of Pandoc’s formats and doesn’t require a large JS download, but it silently truncates inputs to 3,000 characters.
I haven't updated markup.rocks in 5 years, glad to hear it is still useful for others! Reminds me to update Pandoc and switch to https, likely sometime next month. Maybe I can try compiling it to wasm instead of JS this time around.
Let me know if there's anything you'd like to see that would make it more useful for you!
I most often use http://markup.rocks/ for converting HTML to Markdown and for testing that my reStructuredText syntax is correct when contributing to docs.
Pandoc also has a demo web page for trying it out (https://pandoc.org/try/). The demo supports all of Pandoc’s formats and doesn’t require a large JS download, but it silently truncates inputs to 3,000 characters.