A correctly prepared file means the print will look exactly as you intended. A flawed one can ruin an entire project — with no way to fix it after printing. This guide covers everything you need: from file formats to the most common mistakes.
File formats
Print shops accept various formats, but they are not all equal.
| Format | Suitability | Recommendation |
|---|---|---|
| PDF/X-1a | Best for print | Universal standard. Embedded fonts, CMYK, no transparency. |
| PDF/X-4 | Excellent | Supports transparency and ICC profiles. Modern alternative. |
| AI (Adobe Illustrator) | Good | Vector-based. Fonts must be converted to outlines. |
| CDR (CorelDRAW) | Acceptable | Recommended: export to PDF/X before submission. |
| INDD (InDesign) | Acceptable | Send with packaged fonts and images, or export PDF/X. |
| TIFF | For photographs | 300 dpi, CMYK, no layers. |
| JPG | Last resort | Only if nothing else is available. Compression degrades quality. |
Golden rule: When in doubt, export PDF/X-1a. It works every time, everywhere.
Resolution — 300 dpi minimum
DPI (dots per inch) determines image sharpness in print. On screen, 72 dpi looks perfectly fine — on paper, it is a disaster.
- 300 dpi — standard for all printed materials. Business cards, flyers, brochures, books.
- 150 dpi — acceptable for large formats (posters above B2), viewed from a distance.
- 72 dpi — screen only. In print, images will be pixelated and blurry.
How to check: in Photoshop, go to Image → Image Size, Resolution field. In Illustrator: Document Raster Effects Settings. Do not upscale a 72 dpi image to 300 dpi in settings — interpolation cannot create pixels that were never there. The result is a soft, blurry image.
Colour space — CMYK vs RGB
This is the most common cause of disappointment after printing. RGB (Red, Green, Blue) is the colour space of screens — the monitor emits light. CMYK (Cyan, Magenta, Yellow, Key/Black) is the colour space of print — colours are mixed from pigments on paper.
RGB has a wider colour gamut than CMYK. That glowing neon green on screen? In CMYK it will be darker, more subdued. If you submit a file in RGB, the printer converts it automatically — but the result may not match your expectations.
In practice: Always work in CMYK from the start. If you worked in RGB (for web use), convert before submission and check the colours on screen. Pay particular attention to vivid blues, purples, and neon shades — these shift the most in CMYK.
Bleed — the 3 mm rule
Bleed is the extra strip beyond the final trim size that ensures no white edges appear after cutting. Without bleed, you risk a white border on the printed piece — even if the design extends “to the edge”.
Standard bleed: 3 mm on each side. Some printers require 5 mm. Check with your printer or use 3 mm — it covers 95% of cases.
All backgrounds, images, and colour areas extending to the edge must extend 3 mm beyond the trim line. Text and logos must sit at least 3–5 mm inside the edge.
Safety margin
The safety margin is the space between the trim edge and the nearest text or critical element. The cutting blade has a tolerance of ±0.5–1 mm. If text sits too close to the edge, it may be trimmed off.
Recommended safety margin: 3–5 mm inside the trim line. For books and brochures with binding: add an extra 3–5 mm on the spine side, as the paper folds into the binding there.
Overprint and knockout
Overprint means one colour prints on top of another. Knockout means the lower colour is removed beneath the upper one (white space underneath). Why does this matter?
Black text on a coloured background must be set to overprint. If it is not, a white gap appears beneath the black letters — and with even the slightest registration shift, white halos appear around the type.
Coloured elements on another coloured background should be in knockout mode — otherwise colours mix unpredictably.
Most professional applications (InDesign, Illustrator) handle this correctly by default. Problems arise with manual settings or files from unusual software.
Fonts — embedding
The print shop does not hold your font licence. If a font is not embedded in the PDF or converted to outlines, the system substitutes a default typeface — and your design will look as though somebody else made it.
- PDF/X-1a: automatically embeds all fonts.
- Illustrator: Type → Create Outlines (converts text to paths).
- InDesign: include font embedding when exporting to PDF, or export as PDF/X.
- CorelDRAW: export to PDF or convert text to curves (Ctrl+Q).
Verification: open the final PDF on a computer that does not have the fonts installed. If everything looks correct, the file is ready.
Most common mistakes
| Mistake | Consequence | How to avoid it |
|---|---|---|
| File in RGB | Colours differ from expectations | Work in CMYK from the start |
| Resolution under 300 dpi | Pixelated, blurry images | Use the image source at full resolution |
| No bleed | White edges on the print | Add 3 mm bleed on each side |
| Text too close to the edge | Trimmed text | Safety margin of 3–5 mm |
| Fonts not embedded | Substituted typeface, broken design | PDF/X-1a or outlines |
| Black text without overprint | White halos around letters | Set overprint for black text |
| Upscaled image | Soft, unsharp image | Use the original resolution |
Frequently asked questions
What file format should I send?
PDF/X-1a is the universal standard. If you cannot create PDF/X, send a regular PDF with embedded fonts and CMYK colours. For vector graphics, AI or EPS. Avoid JPG — compression degrades quality.
What resolution is required?
300 dpi for all standard printed materials (business cards, flyers, brochures, books). 150 dpi for large formats viewed from a distance (posters, banners). 72 dpi is for web and screen only — it is not enough for print.
What is bleed?
Bleed is the 3 mm extra strip beyond the final trim size. It ensures no white edges appear after cutting. All backgrounds, images, and colours extending to the edge must extend 3 mm beyond the trim line.
Read our complete Printing Guide for a full overview of services, or check the flyer printing guide.
Do not worry, you do not need to be a graphic designer. If you have questions about file preparation, write to us — we are here to help.
More about our print shop.
Posodobljeno: 07-04-2026