Your file must be a high-resolution pdf.
Colour coding in cmyk, not in pantone (printing only in offset) not in RGB (they are only screen colours, so in print you will have a different colour result than on the screen).
300dpi resolution.
5mm chamfers on each side and cut points. All elements of your mock-up (lettering, photos, drawings, logos) must be placed at least 5mm through the cut points. If you want a design or photo to stand out, it should be up to 5mm. outside the cut points.
Fold points if your form folds.
 All fonts and elements of your mock-up should be outlines or curves.
For offset printing, for more correct colour accuracy, we recommend printing a certified digital colour test, it only applies in the case of exclusive printing and this is because in co-printing there cannot always be colour accuracy, the tolerable margin of error in the shade of the colours of the forms that are not accompanied by a certified essay or relate to co-printing is + or - 10%.
Brochure mock-up files, when 2-sided, should be on 2 pdf pages (either separate or in the same pdf).

For the cover of a book as well as for other forms and cards, there are both plain (Velvet, Illustration) and special papers for monochrome or four-color printing such as Acquerello Avorio, Acquerello Bianco, Tintorento Guesso, Tintorento Crema and others.
Indicatively, we list some details:

Acquerello : Papers coated with excellent performance in both four-color and background printing - embossed with fine stripes on both sides. Available in two shades:

• Cream (Acquerello Avorio) in  240g
• White (Acquerello Bianco ) in  240g

Tintorento :Paper with subtle hammering on both sides. It is recommended to be used for four-color printing that do not have large backgrounds, so that the texture of the paper can be seen better. Available in two shades, Sugar (Crema) and White (Guesso) in 250 g.

Natural evolution 280 gr : Coated paper. Thanks to the special coating it has, it is ideal for four-color printing with backgrounds, with excellent color performance. Available in two shades white and ivory (very light sugar).

White matte  : Specially processed European papers for the inner of books. Most books are printed on white  matte paper. For those who want a creamy shade, there are cream papers with equally excellent print quality.

Velvet :Coated paper with a smooth velvet feel and smooth surface on both sides. It has excellent color rendering. It is mainly used in color printing.

You apply online to the national library in order to be allocated an ISBN number for the book and an ISSN number for the journal. Once the publication is complete you must send 4 copies of your book free of charge to the national library.
For more information visit the website: www.nlg.gr
Detailed instructions can be found in the following file Register ISBN New Publisher

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.