Old Hindi fonts are not Unicode
A lot of Hindi documents typed before Unicode still use Kruti Dev, Devlys, or Shree Lipi. The letters only look correct in that font. Paste them into a website, or switch the font to Mangal, and the words fall apart.
These tools remap the characters. You must name the font the text was typed in. Converting Unicode as if it were Kruti Dev scrambles real Hindi. Work on a copy.
If you already know the job, start with Unicode to Krutidev or Krutidev to Unicode.
Every format on the site is listed from the homepage.
Name the font or the words scramble
Open the tool that names your two formats and read what the download will contain before you delete the original. If a result does not match that description, tell us.
Name the font or the words change
Kruti Dev, Devlys, and Shree Lipi stored Hindi in legacy encodings. The letters only look correct in that font. Paste them into a website, or switch the font to Mangal, and the words fall apart. These tools remap characters in the browser. Nothing is uploaded. You must name the font the text was actually typed in. Converting Unicode as if it were Kruti Dev scrambles real Hindi.
Mangal is already a Unicode font. A Mangal tool normalizes text. It does not perform the legacy remap. If the source was Kruti Dev, use the Kruti Dev tool. Shree Lipi on this site converts toward Unicode, not back. Work on a copy. Test one sentence you can read before a whole document. The wrong line looks like Hindi and says something else.
Convert a sentence, set the target font, and read it aloud or compare it to a printout. Then convert the rest. A whole document of scrambled Hindi is hard to undo if you overwrote the only copy. Mangal and Unicode are the web side. Kruti Dev, Devlys, and Shree Lipi are the legacy side. Do not mix those names because the menus sit near each other. Unicode is what a website, a phone, and current Word understand. Legacy fonts are what an old office printer may still require. Convert in the direction the next reader needs, and keep both copies until a person who can read Hindi has checked a full paragraph.
One sentence, then the document
Paste a line you know by heart. Convert it. Set the font the next reader will use. If the line is wrong, stop and pick the other source font. Kruti Dev, Devlys, and Shree Lipi are not interchangeable even though the menus sit together. Mangal and Unicode are the modern side. Converting modern Hindi as if it were Kruti Dev will scramble a correct document.
Keep the original file with its original font installed on one computer until a person who reads Hindi has checked more than the title. Titles are short and can look plausible when the body is wrong. The work stays in the browser. The risk is overwriting your only copy, not an upload.
Print one paragraph from the original font and one from the converted Unicode, and compare them on paper if the document is long. Screen fonts can make a wrong mapping look almost right at a glance. A printed line is slower and clearer. If you must deliver both a legacy file and a web file, name them with the font, not only with the date. The next person will otherwise apply the wrong font and think the conversion failed.