Two different problems, handled differently
A Telugu PDF is either digital — created from a document, with a text layer inside — or scanned, meaning it is images of pages. For a digital PDF the text is already present and the job is extraction: pulling it out without mangling it. For a scanned PDF there is nothing to extract and the page has to be recognised first. Uploading either one here works; the difference matters mainly because a digital PDF converts near-perfectly while a scanned one inherits the accuracy limits of recognition.
Why Telugu PDFs extract badly elsewhere
Many PDFs embed subsetted fonts with no ToUnicode table, so the file records which glyph to draw but not which character it represents. Naive extractors emit raw glyph ids — the (cid:31) sequences you may have seen — or silently drop the text. Others shatter Telugu into one cluster per box, producing a document with a single akshara per paragraph. Some extractors also duplicate combining marks, turning పుట్టుక into a form with doubled matras that looks almost right and is not. This converter re-flows text from glyph positions rather than trusting box grouping, and repairs duplicated marks.
What is preserved and what is not
Paragraphs, reading order and the text itself come through. Font choice, exact spacing and complex multi-column layouts are approximated rather than reproduced — the goal is an editable document, not a pixel-identical copy. Tables and embedded images are handled on a best-effort basis.