Grayscale PDF

Choose Best for text/vector for documents and Best for photos for imagery. Vector mode edits colour operands token by token inside the page's instructions, so the file keeps its fonts, its selectable text, its crisp line art and its original structure — reports, contracts, invoices, code listings and charts all come out the way you would want. Raster mode discards that and replaces each page with a grayscale photograph of it, which is the only reliable option for pages built from gradients, spot inks or indexed palettes. The live preview looks similar either way, so decide on the document type rather than on appearance: if you would miss being able to search the text, stay in vector mode.

Only raster mode turns an embedded colour photograph gray. Vector mode rewrites colour operators — fills, strokes and the shading behind them — but an embedded JPEG or PNG is opaque binary data with its own colour information, and the tool deliberately leaves it alone, so photographs stay in colour while the surrounding text and boxes go gray. Raster mode has no such limit: it renders each finished page and pushes the whole bitmap through a grayscale conversion, so every photo, logo and colour swatch is converted with it. If your document is mostly text but holds one colour photo that also needs neutralising, raster mode is the answer despite the loss of searchable text.

Vector mode stops rather than hand you a file that is still partly coloured. Some colour paths cannot be neutralised by rewriting operands — indexed palettes, Separation and spot inks, and gradient shadings each carry their colour somewhere the content stream does not expose. When the parser meets one of those it aborts, names what it found, and nothing is written to disk, because a half-converted document that still prints in colour at the print shop is worse than a clear failure. The amber panel includes a link that switches you to Best for photos, which flattens every page and therefore always produces a genuinely gray result. Splitting out the offending pages and converting them separately also works, but switching modes is nearly always the simpler route.

Converting to grayscale is not a reliable way to shrink a PDF, and vector mode barely changes the size at all. In vector mode only the numeric colour operands are rewritten; the fonts, images and page structure are otherwise untouched, so the output lands within a whisper of the input. Raster mode replaces each page with a JPEG, which can go either way — a photo-heavy page often gets lighter, while a page of plain text usually gets heavier, since a picture of text costs more than the text itself. If size is the actual goal, run Compress PDF, which is built for that trade-off and refuses to save a result that is not smaller than what you gave it.

A gray PDF and a gray print job are two different things. Many printer drivers mix cyan, magenta and yellow to reproduce a neutral gray unless you explicitly tell them not to, so a page can be perfectly grayscale in the file and still drain colour cartridges. Look for a Black & white, Grayscale or Print in greyscale option in the print dialogue, and on some drivers a separate use-black-cartridge-only setting. Converting the PDF first is still worth doing: it guarantees the document itself contains no colour, which is what a print shop's automatic colour-page counter measures when it decides what to charge you. It also makes the file itself honest about what it holds, which matters whenever somebody else is doing the printing.

Grayscale PDF is free, has no page or file limits beyond your own hardware, adds no watermark, and never uploads anything. Vector conversion runs on pdf-lib and raster conversion on pdf.js plus a canvas filter, both inside the browser tab you already have open, so the document is read from your disk and the converted copy written straight back to it. Nothing is queued on a server and nothing remains once you close the tab. Password-protected files are the one thing that will not open — unlock them with Remove PDF password first, then convert. How long the job takes depends on your own hardware and on the strategy: vector mode walks the content streams, raster mode renders every page, so a long illustrated document is noticeably slower than a short text one.