Invert PDF colors (dark mode)

No, and that is the nice part. Each mode is a full-page rectangle in a blend mode: Difference for a full inversion, Saturation to drain colour, Multiply and Screen for sepia. All of it happens inside the PDF's own graphics model, so text stays selectable and searchable and images keep their original data.

Barely, for three of the four modes: a rectangle and a blend instruction per page is a few hundred bytes. Dark mode is the exception, because it paints the untouched page back over the inverted one to recover the hues, so the page content is carried twice and the file roughly doubles.

For a full inversion, run it again: inverting an inversion returns every channel to where it started. Sepia and grayscale throw colour away, so nothing brings it back. Your source file is never modified either way, and the result is a new document named after the mode you picked.

Because the effect lives in the file as a blend mode instruction rather than as baked pixels. What you see depends on your reader applying that instruction. Blend modes are a standard part of the PDF format, so mainstream readers handle it, but a simple or embedded viewer might not.

Four modes: dark, which inverts the page and puts each colour's hue back so a link stays blue; full invert, the photographic negative; sepia; and grayscale. There is no page range, so if you want only some pages recoloured, extract them first, recolour, then merge.

No. pdf-lib loads the file, draws the rectangles and saves it, all in a Web Worker in this tab. Drop as many PDFs as you like and each comes back as its own recoloured file. Nothing is sent anywhere and the tool runs with your network off.