Guides / how to tell if a pdf is vector or scanned
How to Tell if a PDF Is Vector or Scanned
Knowing how to tell if a PDF is vector or scanned saves you from the worst surprise in PDF to CAD work: waiting for a conversion, opening the DXF, and finding one big picture or a mess of traced blobs where you expected clean lines. The check takes 30 seconds with nothing more than a PDF viewer.
What is the difference between a vector PDF and a scanned PDF?
A vector PDF stores drawing instructions: a line from this point to that point, an arc with this radius, the word “KITCHEN” in Arial at 2.5 mm. AutoCAD, Revit, ArchiCAD and most other CAD programs produce vector PDFs when they plot to PDF. Convert one and every line comes back as a line.
A scanned PDF stores a raster image: a grid of pixels per page, the same thing a photo is made of. A 300 dpi scan of an A1 sheet is 7016 × 9933 pixels, about 70 million dots, and none of them knows it belongs to a wall.
Most of the confusion comes from files that mix the two. Those are covered further down.
How can you tell in 30 seconds?
Run these five tests in order. The first two settle most files.
- The zoom test. Zoom to 1600% or more on a thin line or a small letter. Vector lines stay sharp with clean edges at any zoom. Scanned lines go soft, grey or stair-stepped, and you will see specks and fuzz around them.
- The text test. Press Ctrl+F (Cmd+F on a Mac) and search for a word you can see, such as a room name or “SCALE” in the title block. If the viewer finds and highlights it, the PDF has live text. If it finds nothing, the text is either part of an image or converted to outlines.
- The Fonts tab. In Adobe Acrobat or Acrobat Reader, open File > Properties (Ctrl+D, or Cmd+D on a Mac) and click the Fonts tab. An empty list means no live text anywhere in the file.
- The click test. Open the PDF in Inkscape (File > Open) or Illustrator and click on a line. In a scan, one click selects the whole page as a single image. In a vector file you get individual paths. Inkscape groups imported content, so double-click to enter the group before you judge.
- The scan clues. Look for a grey or yellowish paper tone, a slightly tilted border, punch-hole shadows, folds, handwritten notes, stamps and signatures. One of these alone proves little. Three together mean scanner.
While the Properties window is open, read the Application and PDF Producer fields on the Description tab too. A CAD program or a PDF printer driver there points to vector; the name of a copier or scanning app points to a scan.
What do the results look like side by side?
| Test | Vector PDF | Scanned PDF |
|---|---|---|
| Zoom to 1600% | Crisp edges at any zoom | Blur, pixels, specks |
| Ctrl+F for a visible word | Found and highlighted | Not found (unless OCR was run) |
| Fonts tab | Lists fonts such as Arial | Empty, or one OCR font |
| Click in Inkscape | Separate paths | One image per page |
| Paper look | Clean white background | Paper tone, tilt, stamps |
If you work on the command line, the free Poppler tools give the same answer in one line each: pdfimages -list shows every embedded image with its pixel size, and pdffonts lists the fonts. A page with one full-page image and no fonts is a scan.
What about PDFs that are both?
Hybrid files are common, and they explain most “it converted strangely” complaints.
- Scan plus OCR. OCR (optical character recognition) software lays invisible, selectable text over the scanned picture. Text search works, yet every line is still pixels. The Fonts tab can list a single odd font: files from the open-source Tesseract OCR engine show GlyphLessFont. Treat these files as scans.
- Vector with embedded images. A site plan with an aerial photo underneath, a detail sheet with a manufacturer’s photo, or a title block with a pixel logo. The linework converts as vectors and the images stay images.
- Vector with outlined text. Some PDF exports turn every letter into curves. The zoom test says vector, the text test finds nothing, and the Fonts tab is empty. The letters convert to CAD as polylines instead of editable TEXT, which bloats the file, and you cannot change the wording.
- Printed, then scanned. A vector drawing that someone printed, marked up by hand and scanned back in has become a scan. Ask for the original file before you start tracing it.
- A raster PDF from CAD. Some plot and print settings (printing “as image”, for one) send the whole sheet as one picture, and the result behaves exactly like a scan even though it never touched paper.
Why does it matter for converting to CAD?
The answer decides the whole workflow and how much time it takes.
Vector PDF: you get real CAD geometry. A free PDF to DXF converter puts each colour on its own layer, keeps text as TEXT entities and turns curves into polylines. Your remaining job is scale and cleanup, covered in why a converted PDF is not to scale.
Scanned PDF: the converter traces the ink into outlines. Each pen stroke becomes a thin closed shape made of both edges of the line, so a single wall line arrives as two close parallel edges joined at the ends. That is good enough for laser engraving, sign shapes and a tracing underlay. For a drawing you plan to edit by dimension, plan to redraw the important geometry over the scan. The full workflow is in convert a scanned drawing to CAD, and the converter’s own notes are on the scanned PDF to CAD page.
Hybrid PDF: split the job. Convert the vector part, and treat the raster part (an aerial photo, a hand-drawn markup) as an image to trace or ignore.
What should you do before converting?
- Ask for the source. If the PDF turns out to be a scan, ask the sender for the DWG, DXF or a vector PDF. The original CAD file beats any conversion.
- Check every page. A drawing set can mix both kinds: twenty vector sheets and one scanned survey.
- Note the scale on each sheet before you convert, while the title block is still easy to read.
Thirty seconds of checking tells you whether the next hour goes into cleanup or into redrawing, and that is worth knowing before you quote the job.
Questions people ask
What is the fastest way to tell if a PDF is vector or scanned?
Zoom to 1600% on a thin line or a small letter. A vector PDF stays razor sharp at any zoom, while a scan turns into blurry or stair-stepped pixels.
If I can select text, is the PDF vector?
Not always. Scans that went through OCR carry an invisible text layer on top of the picture, so the text selects while the lines are still pixels. Run the zoom test on the linework as well.
Can a scanned PDF be converted to DXF?
Yes, by tracing. A tracer turns the ink into outlines, and you get both edges of every line as a thin closed shape. That works well for shapes and as a drawing aid, and it needs cleanup or redrawing before you edit dimensions.
Why does my vector PDF have text that will not select?
The text was converted to outlines when the PDF was made. The letters are vector curves, so they convert to CAD as polylines instead of editable TEXT.