The Portable Document Format (PDF) is a file format developed by Adobe System for storing documents. In the printing industry, a special standardized version of PDF (PDF/X) is used which is suitable for coding print-ready files so they are suitable in terms of technology with the processing methods that are customary in the printing industry.
PDF/X standards
| PDF/X version | Contents | Colormanagement | PDF compatibility | Transparency |
|---|---|---|---|---|
| PDF/X-1a (2001) | CMYK + Spot | – | PDF 1.3 | – |
| PDF/X-3 (2002) | CMYK + Spot, kalibrált RGB, Lab | allowed | PDF 1.4 | allowed |
| PDF/X-4 (2007) | CMYK + Spot, kalibrált RGB, Lab | allowed | PDF 1.6 | allowed |
Since our printing house uses a work processes that is calibrated in terms of color management involving the most advanced software based processing methods, we recommend that the standard PDF/X-4 format should be used for submitting print-ready files.
PDF creation
In recent Adobe products (InDesign CS3 or later), you do not need to use PDF distiller to create an intermediary PostScript file as the recent versions of the application can directly generate perfect PDF files. Also, the development of RIP applications used for processing in the printing industry made the processing of “direct PDF files” virtually free of errors. In the following, we are discussing this method of PDF creation. In Adobe InDesign CC, the interface that controls PDF creation can be accessed through the File > Export … menu item when you save the file. In the following, we will examine the key settings in this window.
Recommended settings (General):
Standard
Since PDF/X-4 is a PDF format that was developed specifically for use in the printing industry, this is the format that we recommend in the first place as the selectable parameters in this case are automatically limited so as to prevent PDF contents that are not needed for, or known to impede, the processing for printing (e.g. hyperlinks, bookmarks).
Pages
By default, pages should not be saved as single pages and not as spreads in the PDF file. Spreads should only be submitted in special cases (e.g. jacket design).
Interactive Elements
It is important that the PDF file should not contain any interactive elements (audio, video content or hyperlinks) as they cannot be used in printed form.
Recommended settings (Compression):
Compression Color Images
In order to avoid the unwarranted bloating of files (and to facilitate processing), it is reasonable to reduce the resolution of images so the files do not contain pictures with a resolution higher than 450 dpi (ppi).
Compression
You can select from several compression algorithms to compress your images. If you choose lossy JPEG compression, be sure to select the maximum quality. When JPEG compression, it is not advisable to convert the image more than once, as this may cause continuous quality degradation.
Recommended settings (Marks and Bleeds):
Crop Marks
From the automatic marks, please select the crop marks only! The application will automatically adjust crop marks to the size of the trim box defined in the page settings, which is why it is extremely important to set its size correctly.
Offset
Here you can define the distance of crop marks (from the crop line). We recommend that you set this value to 3 mm in order to prevent closely placed crop marks from extending into the final product.
Bleed
You can set the size of the bleed here, which determines the “extra” area that will be trimmed off the product. See here too.
Recommended settings (Output):
Color Conversion
In this phase, it is advisable to convert all colors to the destination color space (Convert to Destination) in order to avoid adding images to the PDF file that have not been converted from RGB. You can find more details here.
Destination
Here you can set up the ICC color profile describing the output color space. Important! There is no one-size-fits-all setting: you will always need to use a color profile that is suitable for the production technology and the given substrate (paper). Further details are available here.
Profile Inclusion Policy
The PDF/X-4 requires that the ICC color profile of the destination color space should be embedded into the file.
Recommended settings (Advanced):
Subset fonts
Here you can control how subset fonts are embedded by specifying a ratio of the characters used as the limit above which the entire font set will be embedded. Below the limit, fonts are partially embedded as subsets into the PDF file. If the limit is set to 0%, all fonts will be embedded. If the limit is set to 100%, every font will only be embedded as a subset.
Recommended settings (Security):
As password protected PDF files cannot be processed with software applications, the PDF/X-4 standard forbids their use. For this reason, please refrain from using these security measures in other PDF formats too.
Note: The above settings are meant to offer guidelines for creating PDF files correctly for the offset printing technology. However, PDF files created with settings other than the above described ones may also be suitable for processing for printing.