How to convert a PDF to grayscale on a Mac
By Himanshu Ranjan · Updated 8 November 2026
To convert a PDF to grayscale on a Mac, select it and run Convert › Grayscale PDF in FileDial. It saves a new copy beside the original, and links and form fields are flattened. Grayscale suits black-and-white printing and can reduce scan size, and it runs on your Mac without uploading.
What grayscale does, and why people want it
Grayscale means every color is replaced by a shade of gray, from black to white. For a PDF, that is useful in three situations: printing on a black-and-white printer, where you want predictable tones rather than whatever the printer driver chooses; reducing the ink a color-heavy page would use on a color printer; and tidying scans that picked up a color cast from yellowed paper.
It is also a common step before sending a file that will be printed or photocopied by the recipient, such as a form for a court or a school office, because it removes the surprise of a blue highlight turning into a faint gray.
Convert with FileDial
Convert › Grayscale PDF writes a new copy and leaves the original alone.
- Select one or more PDFs in Finder.
- Hold the right Option key to open the dial and choose the Convert category.
- Release on Convert › Grayscale PDF.
- Open the copy and check that colored charts and highlights remain readable.
- Print one page as a test before running a large print job.
What you lose
Color carries meaning in charts and maps. A chart with a red line and a green line may turn into two lines of nearly the same gray, which makes it unreadable. Check legends and any page where color distinguishes categories. Highlighted text becomes shaded text, which is usually fine.
The tool's note says links and form fields are flattened. If the PDF is a fillable form, fill it before converting, or convert a separate copy. This is shared by several FileDial tools that rewrite pages, and it is why keeping the original matters.
- Charts that depend on color may need redrawing.
- Links and form fields are flattened.
- Original stays unchanged beside the copy.
- Convert a copy of fillable forms.
Will it make the file smaller?
Sometimes, but FileDial does not state a size result for this tool, so we will not promise one. The honest answer is to look at the result card, which shows the size before and after. If shrinking is the goal, compress separately: Compress › Compress PDF keeps text selectable with images at 144 dpi, and Compress › Compress PDF (strong) goes to 96 dpi for screen-only use.
Combining the two, grayscale then compress, is a sensible routine for large scanned packs that will be viewed on screen or printed in black and white.
A worked example: a scanned form pack for the printer
You have a 25-page scanned pack that arrived with a pink tint from the scanner. Run Convert › Grayscale PDF on it, and the tint becomes neutral gray, which also looks more professional on a photocopy. If a signature page is in blue ink, it will print as dark gray, which is normally fine for a copy of a signed page.
Next, decide whether the file also needs to be smaller. If you are emailing it, run Compress › Email-safe (under 20 MB) on the grayscale copy. If you are printing it, stop after grayscale and print a single page first to check the contrast. Thin pencil marks and faint stamps can vanish in gray, so look at those pages at full size before you commit a hundred sheets.
Common mistakes
Converting the only copy is the first. The tool writes beside the original, so keep both and delete the wrong one only after checking. The second is converting a fillable form and then wondering why the fields are dead; fill and flatten in the order you intend. The third is assuming grayscale is lossless: shades are computed from color, and two different colors can land on the same gray, which is irreversible in the copy.
The fourth is judging on screen alone. Screens are bright and forgiving; paper is not. A light yellow highlight on a screen can become near-white in print. If the page has highlights you need to see, print a test page, and if a color matters to the meaning, leave that page alone and print it in color.
Grayscale, black and white and dark mode are different
Black and white in the strict sense means only two tones, with no grays, which is what a fax or a photocopier at its harshest setting produces. Grayscale keeps the shades. If you want the strict version, a scan at a bitonal setting does it at capture; converting afterwards cannot recover missing detail.
If your real aim is reading at night, Convert › Invert colors (dark mode) turns white to black while text stays selectable; that is a separate tool with a separate purpose.
Preview's Export dialog has a Quartz Filter pop-up, which Apple documents for the Reduce File Size choice. Other filters may be listed there depending on your macOS version, but we cannot give you documented steps for a grayscale one. Printing offers a black-and-white option in the print dialog of most printers, which changes the print without changing the file.
Documents you print in grayscale tend to be official: forms, statements, applications. FileDial converts on your Mac with Wi-Fi off and keeps the original.
Questions
Does converting a PDF to grayscale keep text selectable?
The note for Convert › Grayscale PDF says it saves a new copy and flattens links and form fields; it does not say text becomes a picture. Open the result in Preview and try selecting a line to confirm that for your own file.
Can I convert a PDF to grayscale to save printer ink?
Yes, that is a common reason. The converted copy prints every page in gray tones, so the content does not need colored ink. Choosing black and white in the print dialog gets a similar result without making a new file. Check the result before relying on it.
Why did my chart become unreadable in grayscale?
Two colors can map to nearly the same gray, so lines or bars that differed only by color blend together. Check charts before you print. If needed, redraw the chart with patterns or different line styles, or print that page in color.