Convert CDX to PNG

ChemDraw structures are exported to PNG when a manuscript system, presentation, web page, or image editor needs a standard image instead of an editable .cdx document. PNG also provides a fixed rendering for sharing chemical diagrams with recipients who do not use ChemDraw.

What CDX files contain

CDX is an ambiguous file extension. It most commonly denotes the binary native format of ChemDraw and ChemOffice, used for chemical structures, reactions, annotations, atom labels, stereochemistry, and editable page layout. Keep this source file because it retains chemical objects and drawing information that PNG cannot preserve.

A separate legacy CorelDRAW compressed-drawing format has also used .cdx. ChemDraw CDX and CorelDRAW CDX files are not interchangeable, so identify the creating application before selecting software or an online service.

Why PNG is used

PNG is a lossless raster format supported by browsers, office software, publishing systems, and image editors. It supports transparency and preserves thin bond lines, wedges, superscripts, and text more cleanly than JPEG, whose lossy compression can introduce visible artifacts around line art.

PNG contains pixels rather than editable chemical structures. It does not retain molecular connectivity, searchable structure data, reaction metadata, or editable labels.

Exporting ChemDraw CDX files

1. Open the file in ChemDraw using File → Open.
2. Check the intended final layout before export. Correct clipped atom labels, overlapping objects, page boundaries, and bond-line thickness at the final display size.
3. Use File → Export and select PNG. The exact menu wording and available export options vary by ChemDraw release.
4. Set the required pixel dimensions. For print placed at a known physical width, calculate pixels as width in inches multiplied by the required ppi; 85 mm at 300 ppi is about 1,000 pixels wide, while 170 mm is about 2,000 pixels.
5. Select a transparent background only when the receiving application supports and needs it; use white for predictable appearance in word processors and print workflows.
6. Open the exported PNG at 100% size and inspect atom labels, charges, stereochemical wedges, arrows, and small text.

Use 300 ppi as a common print-production target when a publisher specifies it, but pixel dimensions determine raster detail; the ppi value stored in a PNG mainly affects its default physical size in layout software. Do not enlarge a small PNG after export.

Other conversion options

For automation, Open Babel can read many ChemDraw CDX files and write a PNG depiction when the installed build includes PNG/Cairo output support:

obabel input.cdx -O output.png --gen2d

--gen2d generates two-dimensional coordinates when needed. Open Babel may not reproduce ChemDraw-specific fonts, page layout, reaction arrows, or complex annotations exactly, so use ChemDraw for publication artwork and compare the output with the original.

CloudConvert and Zamzar offer browser-based CDX-to-PNG conversion, but confirm that the service identifies the upload as a ChemDraw CDX file rather than a CorelDRAW format. Upload only non-confidential files; public conversion services are unsuitable for unpublished structures, regulated data, or client material unless their privacy and retention terms meet the required policy.

For a legacy CorelDRAW CDX file, open it with the compatible CorelDRAW version or a verified legacy importer, then use File → Export to select PNG and set the pixel dimensions. General image editors normally do not open either CDX variant directly.

Compatibility and quality limits

PNG cannot be restored to a chemically editable CDX file without redrawing or chemical structure recognition. Recognition tools can misread atom labels, charges, bond orders, and stereochemistry.

Retain the original .cdx file and export a vector PDF, SVG, or EPS file as well when a publisher or print workflow accepts vector artwork. A vector export scales without rasterizing bond lines and text, while PNG is appropriate where a fixed bitmap is required.