For standard linework with bold lines and clear contrast, 300 DPI is the accepted minimum. For drawings with fine detail, faint pencil lines, hatching, or small annotation text, target 400–600 DPI. Higher DPI captures more geometry information but also increases file size and processing time. Avoid exceeding 600 DPI without a clear reason — noise also scales up.

A drawing placed even 2–3° off-axis on the scanner will produce diagonal lines that should be horizontal or vertical — and the converter will faithfully reproduce the error. Use your scanner's deskew feature or post-process in software like GIMP or ScanTailor. Despeckle to remove dust and paper grain. Crop tightly to the drawing border to eliminate blank white space that inflates file size without adding value.

For linework-only drawings (floor plans, mechanical drawings, site plans), scan in black and white / 1-bit mode. This produces the highest contrast, smallest file size, and cleanest input for vectorization algorithms. Use grayscale only when the drawing contains shaded areas or tonal information that must be preserved. Avoid color scanning for linework — it introduces compression artifacts that the tracer misreads as geometry.

If your "scan" is actually a PDF that was originally created digitally, it may already contain vector geometry. Use AutoCAD's PDFIMPORT command to extract linework directly into a DWG. The result is clean, scaled geometry with no tracing artifacts. Always check first — open the PDF and try to select individual lines. If you can, it's vector. This route bypasses tracing entirely and produces the highest quality output with minimal cleanup.

True paper scans require raster-to-vector tracing. Tools range from AutoCAD's built-in RASTERDESIGN workflow to dedicated apps like VectorizeAI, Scan2CAD, or Inkscape's autotrace. The output will always require cleanup — expect duplicate lines, broken polylines, and misread text. Budget time for CAD cleanup as part of the workflow, not as an exception. This is the most common route for legacy archive conversion projects.

When the original drawing is lost and only the physical part or structure exists, you must reverse-engineer the geometry from scratch. Use calipers, measuring tapes, or 3D scanning to capture real dimensions. At least one verified reference measurement is non-negotiable — you cannot construct accurate CAD from proportion alone. This route is the most labor-intensive but produces the most accurate and fully parametric output when done properly.

Modern AI workflows aim to output editable DXF/DWG with real text objects — not dimension "scribbles" that are merely vector traces of letterforms. Machine learning models trained on engineering drawings can distinguish annotation text from geometry, recognize standard symbols, and classify line types with far greater accuracy than rule-based tracers. The result is a file with actual MTEXT entities, associated dimension objects, and structured blocks rather than a sea of undifferentiated lines.

Centerline extraction is the correct approach for engineering linework. Instead of tracing both edges of a printed stroke (producing two parallel lines per mark — a contour trace), centerline algorithms find the single medial axis of each line and produce one meaningful entity. This directly maps to how CAD geometry is intended to work: one line represents one edge, one wall, one dimension leader. Contour tracing doubles entity count and creates closed slivers that break snapping and area operations.

The fastest production workflow is now: Upload → Convert → Preview Spot-Check → Download → Open in CAD → Re-edit What Matters. Browser-based converters handle the bulk transformation in seconds or minutes; your CAD session focuses only on the semantically important corrections — layer sorting, dimension verification, and text confirmation. This loop is dramatically faster than manual redraw and produces a far more editable baseline than legacy desktop tracing tools.