Getting a PDF ready to print

Page size, margins and bleed

A PDF page has a size recorded in it, and a printer will either honour it, scale it, or crop it. A file laid out for US Letter printed on A4 comes out scaled slightly, which is why the margins look wrong and the font looks a fraction small. PDF page size and orientation covers that mismatch; Resize PDF fixes it properly.

Two ideas do most of the work here. Bleed is artwork extended past the edge of the finished page, so that when the stack is trimmed — and the trim is never exact — there is no white sliver along the edge. Anything meant to reach the edge must run past it. The safe area is an inset margin inside which all text and anything else you cannot afford to lose must sit, for the same reason in reverse.

Home and office printers add a constraint of their own: they cannot print to the edge at all, and will silently shrink the page to fit their unprintable margin. If a document must come out at exact size, design it with real margins rather than fighting the printer.

Colour, and why it looks different on paper

A screen makes colour by adding light. Paper makes it by absorbing light with ink. The two cannot reach the same set of colours, so a bright screen blue or a vivid green will print duller, and there is no setting that fixes it — the ink simply does not go there.

Commercial printing normally wants CMYK, and a print shop that asks for PDF/X is asking for colour and geometry to be pinned down explicitly. For an office printer, leave the file as it is; the driver converts, and it converts adequately.

Printing in black and white is worth doing deliberately. Letting a printer convert colour to grey gives you whatever its driver decides, and coloured text can come out as nearly indistinguishable greys. Converting first with PDF to grayscale shows you the result before it is on paper, and usually makes the file smaller as well.

Fonts and resolution

Fonts must be embedded. If they are not, the printer substitutes, and substitution changes letter widths and therefore line breaks — a document that reflows on the way to the press. This is the same failure as a PDF looking different on another computer, with a more expensive outcome.

Images need roughly 300 pixels per inch at final size. A photograph 600 pixels wide is fine at 5 cm and poor at 15 cm; the file cannot tell you which it is, because resolution only means something once you know the printed size. Screen graphics at 72 DPI look sharp on a monitor and soft on paper, and nothing can add the detail back.

This is the one place where compressing a file can genuinely hurt. Compression works mostly by reducing image resolution and re-encoding, which is invisible on screen and visible in print. Compress the copy you email; send the printer the full-quality file.

Before you send it

• Page size is the finished size, on every page. Check with Page count and file info.
• Orientation is right on every page, and saved rather than viewed — see why a rotated PDF reverts.
• Nothing vital near the edge, and bleed where artwork must reach it.
• Fonts embedded.
• Images sharp at final size.
• Flattened if it contains form fields or annotations, so the printer is not interpreting them — see what flattening does.
• Print one page at home first. It catches more problems than any amount of checking on screen, and it costs one sheet of paper.