Scanned PDF to CAD
A scanned drawing holds a picture of the paper, not lines. The converter traces the ink of each scanned page into outlines and saves them as DXF, so you have something to snap to and redraw over in AutoCAD or any CAD program.
What does tracing give you?
| On the scan | In the DXF |
|---|---|
| Wall lines, outlines, hatching | Closed outlines around the ink, on layer PDF_000000 |
| Text and dimension figures | Outlines of the letters, not editable text |
| Circles and curves | Smooth outlines that follow the ink |
| Dust, stains, faint pencil | Tiny specks are dropped; larger marks come across as shapes |
Tracing is a starting point, not a finished drawing. The positions are right to about half a pixel of the scan, so a plan scanned at 200 dpi is accurate to roughly 0.1 mm on paper. Real-world accuracy then depends on how straight the paper went through the scanner.
How do you convert a scanned PDF to CAD?
- Drop the PDF into the converter. It checks each page and says when a page is a scan.
- Leave "Trace scanned pages" on. The page is rendered at up to 200 dpi and the ink is traced into outlines.
- Set the scale with a dimension you can read on the scan, so the outlines come out at real size. See how to scale a PDF drawing.
- Convert and open the DXF. Put the traced layer on a pale colour, lock it, and draw the lines you need on a new layer.
When is tracing the wrong answer?
When anyone still has the original. A PDF printed straight from AutoCAD, Revit or ArchiCAD converts into clean lines and editable text in seconds, and the DWG itself is better still. Ask the architect, engineer or supplier for either before you trace a scan. For old paper archives with no digital source, tracing saves hours of measuring and redrawing.
Questions about scanned drawings
Can a scanned PDF become a real CAD drawing?
Partly. Tracing turns the ink into outlines you can snap to, measure and redraw over. It does not know that a wall is a wall or that 3600 is a dimension, so a clean CAD drawing still needs someone to redraw the important lines.
How do I know if my PDF is a scan?
Zoom in far. Lines in a vector PDF stay sharp at any zoom; a scan turns blocky or blurry. You also cannot select text in a scan. The converter checks every page and tells you.
Why does every line come out double?
A line on paper has a width. Tracing follows both edges of the ink, so a single wall line becomes a thin closed outline. Snap to one edge, or use the outline as a guide and draw one centre line over it.
What resolution does the scan need?
At least 200 dpi, black on white, straight on the page. Pale pencil, coffee stains and folds turn into stray shapes, so a clean scan saves more time than any setting.