Digital and scanned PDFs take different routes
If your Hindi PDF was made from a document it already contains text, and conversion is a matter of extracting it faithfully. If it is a scan, the pages are images and must be recognised first. Both work here. A digital PDF converts near-perfectly; a scanned one carries the accuracy characteristics described on our Hindi OCR page.
The legacy font problem
A great deal of older Hindi material was typed in pre-Unicode fonts such as Kruti Dev or Chanakya, where the bytes stored are not Devanagari code points at all — they are Latin characters that happen to draw Devanagari shapes in that one font. Copying such text into any other application produces nonsense. If your source is a legacy-font document rather than a scan, our font converter handles that conversion directly, which is a different operation from OCR and lossless where it applies.
What survives conversion
Text, paragraph breaks and reading order are preserved. Fonts and precise layout are approximated. The result is meant to be edited, not to be a facsimile of the original page.