Convert a Scanned PDF to JPG

What makes a scanned PDF different

A scanned PDF is a wrapper, not a document. The scanner photographed each sheet and produced a bitmap — one image per page — and the PDF format stores those images with a little page geometry around them. There is no text, no font and no vector line: where a PDF exported from Word holds instructions for drawing characters, a scanned PDF holds a picture of them.

That changes what a converter can do. Rendering an ordinary PDF is a drawing operation, so its text stays crisp at any size. Rendering a scanned PDF is an image operation: the renderer decodes the stored bitmap and draws it onto the canvas, which is what a viewer such as Firefox or Preview does on screen as well. Nothing is invented along the way, so the output can never contain more detail than the scan itself.

Some scanned PDFs also carry an invisible text layer, added by recognition software so the page can be searched. That layer does not change the picture, and it does not travel into a JPG: the image you get is the scan.

• One stored image per page, wrapped in PDF page geometry.
• No text, fonts or vectors, so sharpness is fixed by the scan rather than by the converter.
• A searchable text layer left by OCR is invisible and is not exported into the JPG.
• Scans are heavy: a colour A4 page at 300 DPI is about 8.7 megapixels, which is why such PDFs run to tens of megabytes.
• A password-protected scan behaves like any other protected PDF — the converter asks for the opening password and checks it on your device.

Choosing the right DPI for scanned pages

The DPI setting decides how many pixels the page is drawn at, and nothing else. Matching it to the scan reproduces the page exactly: an A4 sheet scanned at 300 DPI holds about 2480 × 3508 pixels, and rendering it at 300 DPI produces an image of that same size, pixel for pixel.

Rendering higher than the scan does not recover detail. At 600 DPI an A4 page becomes 4961 × 7016 pixels, roughly 35 megapixels — four times the pixels of a 300 DPI scan for no extra sharpness, because the renderer is enlarging an image it already holds. A page that large also exceeds the area a browser can safely draw in one canvas (about 24 megapixels), so the converter reduces the resolution and tells you it has.

For scanned text, 300 DPI is the setting to use: it keeps small print legible, gives later text recognition the most to work with, and stays inside the canvas limit.

• 300 DPI matches a typical office scan of A4 or Letter paper almost exactly.
• Anything above the scan’s native resolution is upscaling: more pixels, no more detail, much larger files.
• JPEG compression quality matters as much as DPI on text — leave it high when the page is mostly small print.
• A colour scan at 300 DPI is about 8.7 megapixels per page, so a twenty-page document is a genuinely large job; the converter renders one page at a time to keep it manageable.

Convert the scanned PDF step by step

The workflow is the same as for any other PDF — only the settings differ. Everything happens inside the tab: nothing is uploaded, and the scan is never handed to an OCR service or any other server.

1. 1Add the scanned PDF with Choose PDF Files, or drag it onto the drop zone. Large scans are read locally, so the first preview can take a moment.
2. 2Choose the pages you need. Every page is selected by default; a range such as 1-12 keeps a long scan manageable.
3. 3Set Image quality to High quality (300 DPI). On text-heavy scans, leave the JPEG compression at its high setting.
4. 4Press Convert to JPG and follow the progress line — one page is rendered at a time, and the panel names the page in hand.
5. 5Download the pages individually, or press Download all as ZIP to take the whole document in one archive.

• If the converter reports that it lowered the resolution, that page was larger than a browser can draw in one canvas — 300 DPI for the same document avoids it.
• Cancelling part way keeps the pages already finished, so a long scan can be converted in batches.
• A scan of a printed page comes out on a white background exactly as the renderer drew it: no cropping, rotation or straightening is applied, so straighten a skewed page before scanning if it matters.

When the output looks blurry

If a converted page looks soft, the cause is almost always the scan rather than the conversion. The renderer can resample the pixels the PDF holds, but it cannot add detail that was never captured — an image of a page enlarged is still an image of a page.

The usual sources of a soft result are worth checking in this order.

Read more: PDF to JPG quality, DPI and file size

• A low-resolution scan. Material scanned at 150 DPI, or faxed and re-saved, has little detail to begin with; rendering it at 300 DPI yields bigger, softer pixels rather than sharper text.
• Lossy compression applied by the scanner. Many scanners write JPEG data into the PDF at a modest quality to keep file sizes down, and those artefacts are baked into the page before the converter ever sees it.
• Rendering above the native resolution. Asking for 600 DPI on a 300 DPI scan gives four times the pixels and the same amount of information — and a page that large can be capped by the browser canvas limit as well.
• A compression setting that is too aggressive. The output JPEG quality is chosen in the converter: at 70% fine print loses its edges, while 95% keeps them.
• A skewed or faint original. A sheet fed in at an angle, or printed in pale grey, is soft in the scan itself, and no converter setting restores it.