Converting a color PDF to black and white — or more precisely, to grayscale — is useful for reducing file size, preparing a document for black-and-white printing, meeting a submission requirement, or simply making content more readable in certain contexts. There are several ways to do it, each with slightly different results.
Grayscale vs True Black and White
"Black and white" in everyday usage usually means grayscale — a range of tones from pure black through greys to pure white. True black and white (also called 1-bit or bilevel) means every pixel is either fully black or fully white with no intermediate tones. The distinction matters:
- Grayscale: preserves tonal variation — photographs look natural, gradients render smoothly, shadows have depth. Files are smaller than color but larger than true black and white. Best for documents with photographs or complex graphics.
- True black and white: very small files, sharp text rendering, but photographs look harsh — grey tones are simulated through dithering patterns. Best for text-only documents or simple line art.
For most use cases, grayscale is what people want. The methods below produce grayscale output unless specified otherwise.
The Quickest Method: Print to PDF in Grayscale
Any PDF viewer can convert a color PDF to grayscale by printing it to a new PDF with grayscale settings:
- Open the PDF and press Ctrl+P (Windows) or Cmd+P (Mac)
- Select Save as PDF or Microsoft Print to PDF as the printer
- Look for a color option — in some dialogs it's under Properties or More Settings
- Select Grayscale or Black and White
- Save — the new PDF is in grayscale
The grayscale option isn't always visible in the basic print dialog — look for it in the Advanced or Properties section. In Adobe Reader specifically, the Advanced print settings include a "Print Color as Black" option that achieves this.
Adobe Acrobat Pro: Convert Color to Grayscale
Acrobat Pro has a dedicated color conversion tool that produces cleaner results than the print method:
- Go to Tools > Print Production > Convert Colors
- In the Convert Colors dialog, set the Conversion Attributes to convert to a grayscale color space — typically Device Gray or a grayscale ICC profile
- Apply to the whole document and save
This method converts color data in the PDF's internal structure rather than re-rendering through the print path. The result typically preserves more of the document's features — bookmarks, hyperlinks, form fields — compared to the print method. It also allows more precise control over which color spaces to convert and which to leave unchanged.
On Mac: Preview's Quartz Filter
Mac Preview has a built-in grayscale conversion option through its Quartz Filter system:
- Open the PDF in Preview
- Go to File > Export as PDF
- Click the Quartz Filter dropdown and select Gray Tone
- Save — the exported PDF is in grayscale
Preview's Gray Tone filter is straightforward and works well for most documents. One limitation: the Quartz Filter sometimes increases file size rather than decreasing it due to how it reprocesses the image data. Check the output file size — if it's larger than the color original, use a compression tool afterward.
File Size After Converting to Grayscale
Grayscale PDFs should be smaller than their color equivalents because each pixel requires one byte of data instead of three (for RGB color). In practice, the size reduction depends on how the conversion is implemented and what else changes in the process.
For maximum size reduction, run the grayscale PDF through a PDF Compression tool after conversion. The combination of removing color data and then compressing the result typically produces the smallest possible file size. WukongPDF's compression tool at www.wukongpdf.com handles this final step — upload the grayscale PDF, apply medium compression, and the resulting file is both grayscale and optimally compressed.
When You Shouldn't Convert to Grayscale
Color carries meaning in some documents — charts where different data series are distinguished only by color, maps with color-coded regions, diagrams where color indicates different states or categories. Converting these to grayscale makes the color-coded distinctions invisible or ambiguous. Before converting, check whether any information in the document depends on color to be understood. If it does, either keep the color version or redesign the color-dependent elements to use patterns or labels as additional differentiators alongside color.