How to prepare files for print

A good print file is a PDF at final trim size, with bleed, images at 300 ppi at the size they'll print, CMYK colors on the profile your printer asks for, and embedded fonts. Printers usually want it as PDF/X. Run through the list below and the file passes their check the first time, instead of costing you a day of "could you resend it, please" emails.

Here's the order we check files in before they go to press.

1. Size, bleed and safe zone

Set the document up at final trim size, the size after cutting. Then add bleed on top: backgrounds and photos that touch the edge need to run past the trim line, so a slight shift of the blade doesn't leave a white sliver. Adobe's documentation gives 3 mm (0.125 in) as the typical industry value and, rightly, tells you to check with your printer. Some ask for more, for example on banners or anything that gets folded.

The opposite goes for text, logos and QR codes: they stay inside the safe zone, a few millimeters in from the trim line. Your printer tells you how much. We explained all three lines, with a drawing, in the post on bleed, safety margin and trim line.

Only add crop marks if the printer asks for them. Many add their own.

2. Resolution: 300 ppi at actual size

For print, images need about 300 pixels per inch at the size they appear on paper. InDesign's print presets (Press Quality, PDF/X-1a) downsample color images to exactly 300 ppi, which tells you where the usual target sits.

The math is simple: width in millimeters divided by 25.4, times 300. A photo covering the full width of an 85 mm business card needs about 1,000 pixels across. The same photo on an A2 poster would need more than 4,900.

A logo taken from your website and scaled up in the print file almost never makes it. Logos and text go in as vectors (PDF, AI, SVG) so they stay sharp at any size.

3. Color: CMYK on the printer's profile

Screens show color in RGB; a press lays down four inks (CMYK). You convert using the printer's ICC profile, not one picked at random.

For offset, the most common profiles come from the ECI (European Color Initiative):

Both came out in 2015 for the 2013 edition of the offset printing standard, ISO 12647-2. Plenty of printers still work on the previous generation, ISO Coated v2. Don't guess: ask which profile they want and convert to it. For digital printing, ask whether they want the file already converted or prefer to do the conversion themselves.

Spot colors (Pantone) stay as spot only if the job really prints with that separate ink, say an exact brand color on a long run. Otherwise, convert them to CMYK and check how they look, because some Pantone colors don't have a faithful four-color equivalent.

4. Black and thin lines

Small black text should be black only (100K), not a mix of four inks. It's a single ink, so it can't end up with colored fringes when the plates shift slightly on press.

For large black areas (a background, a huge headline), 100K on its own can look gray. That's where you use a rich black, with a little of the other inks underneath. Ask your printer for the recipe: they know how much ink their paper and press can take.

Very thin lines and very small type can break up or vanish in print. The minimum depends on the printing method and the paper, so ask, especially for white text on dark backgrounds or for foil.

Overprint is a setting that tells an element to print on top of the color underneath instead of knocking it out. The top ink goes over the bottom one, like a transparent ink. It's useful for small black text. On a white element it's a trap: white isn't an ink, so white text set to overprint simply doesn't show up. Check it in the overprint preview in Acrobat or InDesign.

5. Fonts and the PDF format

Fonts get embedded in the PDF or, for logos and headlines, converted to outlines. Otherwise the printer opens your file with a substitute font and your layout shifts.

The format usually requested is PDF/X, a family of ISO standards for exchanging print files. The two you'll run into:

• PDF/X-1a: the older, safe option. CMYK and spot colors only, fonts embedded, transparency flattened, with bleed and marks included.
• PDF/X-4: standard ISO 15930-7, built on PDF 1.6. The file contains everything needed for print, color profile included, and PDF 1.6 keeps transparency live instead of flattening it.

Which one? Whichever your printer asks for. If they send a settings file (.joboptions), load it into InDesign or Illustrator and export with it.

6. The final check (preflight)

Before sending, open the PDF and check it. InDesign has a Preflight panel that flags problems while you work, and Acrobat Pro has an Output Preview where you can see the color plates and overprint. The table below is our basic pass.

If you don't have time for all of this, we prepare print-ready files, ready to send to the printer, for any job at Optical Merch & Print.