How PDF to Markdown works: a whole converter in your browser.

A PDF is a stubborn thing to read by machine. It records where every glyph sits on a page, in what font and size — but not that one line is a heading and the next three are a paragraph. The PDF to Markdown converter rebuilds that lost structure heuristically, and it does the whole job in your browser. This post covers what it can do, then opens the hood on how the conversion actually works.

What the converter does

Everything below happens on the page you have open — there is no upload step, no processing queue on a server, and no account.

Add a PDF any way you like

• Drop, browse, or paste. Drag files in, click to browse, or paste a copied PDF with Ctrl/Cmd + V. Documents up to 100 MB each are supported.
• Batch, safely. Drop a whole folder and the files queue up. They convert one at a time so a big batch never freezes the tab, each showing its own waiting, converting, and done status.
• From a URL — even CORS-blocked hosts. Paste a link and it fetches in your browser. When a host blocks cross-origin downloads, a small same-origin proxy retrieves the public file so the conversion still works. One-click sample PDFs let you try it instantly.

Structure it rebuilds

• Headings reconstructed from font sizes, so chapter and section titles keep their hierarchy.
• Lists — bulleted and numbered lines become proper Markdown lists, with ordered lists keeping their original numbering.
• Cleaner text — repeated page headers, footers, and standalone page numbers are stripped; wrapped and hyphenated lines are stitched back into flowing paragraphs; bold and italic runs are re-emphasized; bare URLs are auto-linked.

Read it, check it, export it

• Side by side. Open the original PDF in a panel beside the Markdown to proofread the result page by page.
• Preview or raw. Flip between a rendered preview and the raw Markdown, or expand the workspace to fullscreen.
• Export. Copy it, download the .md, print it, or open it in the full Markdown Viewer editor.

How it works: from PDF to Markdown in six passes

The converter feeds on the text content pdf.js extracts for each page: positioned text runs, each a bit of text with a transform matrix (where it sits), a width, and a font reference. From that raw material, six passes rebuild a document.

1. Resolve fonts to emphasis. Each font is mapped to an inline format — bold or italic — from its name. The font whose glyphs cover the most text is treated as the plain body face, so a document set entirely in a …-Bold body font does not come out all bold.
2. Group runs into lines. Runs are gathered into visual lines by baseline (vertical) proximity, keeping each run’s formatting as a segment of the line.
3. Drop page furniture. Short lines near the top and bottom edges are fingerprinted; anything repeated across most pages — running headers and footers — or matching a page-number pattern is removed.
4. Learn the body size and spacing. The most common font size becomes the body baseline, and the typical line spacing is measured — the calibration that makes paragraph detection work across different documents.
5. Map sizes to headings; find lists. Sizes larger than the body baseline map to heading tiers (H1–H6), and bullet (•, -) and numbered (1.) markers are detected as list items.
6. Rebuild paragraphs, emit Markdown. Consecutive body lines are merged into paragraphs — repairing words split by a hyphen at a line break — then written out as Markdown with inline **bold** and _italic_ and auto-linked URLs.

Why font size, not tags

This is the crux of every PDF to Markdown converter. A web page has <h1> and <ul> elements that say what each block is. A PDF has none of that. It has a glyph placed at an x/y coordinate, in a named font, at a size — pure visual layout. The only reliable signal that a line is a heading is that it is bigger than the text around it, so the converter learns each document’s own body size rather than assuming a fixed number.

The same reasoning drives the small repairs that make output readable. A PDF wraps a paragraph across many short lines with no marker to say they belong together, so the converter re-joins body lines using the measured line spacing. When a line ends in conver- and the next starts with sion, it removes the hyphen and fuses the word; across a page break, a paragraph only continues when the sentence was left unfinished.

Where it runs — and what stays private

The parsing engine is Mozilla’s pdf.js, which reads the document inside a Web Worker in your tab. The conversion logic itself is pure and framework-agnostic — it takes the extracted text and returns a Markdown string, and is unit tested without pdf.js at all. Your file is read locally and converted locally.

The honest limits

Because structure is reconstructed from visual cues, some inputs are genuinely hard:

• Scanned PDFs are images of text with nothing to extract — run them through OCR first.
• Password-protected PDFs can’t be parsed; remove the password first.
• Complex multi-column layouts and heavy tables may need manual cleanup. Simple, single-column documents convert very cleanly.

Frequently asked questions