The pdf must be of high resolution
In case of pdf from Corell, the fonts should be converted into curves.
In the case of pdf from Illustrator, the fonts should be converted into outlines.
In case of creating a pdf from Photoshop, it is more correct to work on the file in its actual size (i.e., 8x5cm or 9x5cm), at a resolution of 300dpi and in CMYK colour scale and not RGB.
Don't forget RGB colours are screen and not print. Colours should preferably be selected from a printed four-color scale. Special care should be taken when using raster. It is preferable that every colour we use is neutral, but if you want to use a certain percentage of a certain colour, it should not be less than 15%. (If your work has a grey colour, i.e. a percentage of black, it is better to come out of a four-color e.g. for 50 % black match C 20%, M 20%, Y 20%, K 30%).
Also, in digital printing we do not choose Pantone colour (for offset exclusive printing).
When 2 sides are desired, each side must be on a separate page and in the same position.
Your files should have cut points and bleed margins of at least 5mm on each side. All elements of your mock-up (lettering, photos, drawings, logos) must be placed at least 5mm through the cut points.
Closed pdf files do not allow interventions and corrections. If you still have the fear of the "printer's demon", we recommend checking a proof before final printing.