Originally developed for office communications use, the PDF file format is now the world standard for electronic document exchange. A PDF file’s unique characteristic – the ability to exist independent of the hardware, software and operating system used to create it – allows file creators to share documents and to keep them secure from modification.
PDF version 1.0, an internal project of Adobe Systems conceived by founder Dr. John Warnock and based on the page description language PostScript, was first announced at Comdex Fall 1992 where it won the “Best of Comdex” award. After years of continuous improvement, and in recognition of the power of PDF for document exchange, Adobe relinquished control of PDF to the International Organization for Standardization (ISO) in 2008.
For printers, PDFs solve many problems associated with using customer-prepared files. Before PDF, printers had difficulty opening and preparing files that were created using many kinds of software programs and containing fonts not owned by the printer. This led to delays in getting on press, extra cost for file repair, and frustration for both customers and the printer.
By using PDF as the standard for submitting files, customers can use any platform and their favorite software program to create files. Printers can accept the files and prepare them for output to press plates or for digital printing knowing that the finished page images will be what the customer expects.
A good PDF file begins with a good native file
As versatile as a PDF file is, the final printed product will only be as good as the native application file. A PDF created from a poorly-designed file containing low resolution photographs or graphics and typographical or grammatical errors will still have these flaws. And a PDF created from a file that has no allowance for bleeds (i.e., an image that extends beyond the trim line) or finishing functions (binding, drilling, saddle stitching, etc.) will still need to be repaired and resubmitted.
Here are a few tips to help you create good native application files:
• Set the page size equal to the document’s final page size after trimming.
• Set the live print area of the page to create a minimum of ¼’ of white space on top, bottom and side margins.
• Extend any image that will bleed to beyond the trim line. The standard allowance for a bleed is 1/8 inch (0.125), so if the final size of the printed piece is 8.5 x 11, then set the document size at 8.75 x 11.25, set trim marks at 8.5 x 11, and extend the image that will bleed 0125 inches past the trim lines.
• Set trim, score and fold marks outside live print area.
• Make allowances for finishing operations such as folding, drilling and binding.
• Use images of 300 dpi resolution at the size they will appear in the document. Lower resolution will produce pixelated images; higher resolution will increase file size without improving print quality.
• Use Tagged Image File Format (TIFF) for photographs rather than JPEG or GIF.
• If printing a color photograph in black, save as grayscale before placing the image in the document.
• Crop images in an image editor such as Adobe Photoshop or Illustrator.
• Set screens and tints at a minimum of 5% and maximum of 95%.
• Use the correct color space for the output (CMYK or Pantone for offset printing).
• Delete blank pages before creating the PDF.
• Use the right native application. For complex page layout, use printing-standard programs like InDesign or Quark XPress. Use Publisher and Word for simple layouts such as one-page flyers. Avoid using non-page layout programs such as Photoshop, Illustrator, PowerPoint, or Excel.
Preparing a PDF file for print
Before a PDF file can be used for printing, it must go through a process called preflight. There are two parts to preflight. Content preflight, completed by the customer, confirms that all necessary components of the file are present, including placed graphic images, fonts, bleeds, and correct color assignment. Content preflight also includes spellcheck and proofing.
Technical preflight, completed by the printer, examines how the file is constructed and assesses whether it is ready for raster image processing – converting fonts, line art and photographs into dots. During technical preflight, we check image resolution, color assignment, color separations, allowance for bleeds, trapping values, trim and paper sizes. We also impose multi-page documents into printer spreads so that pages will back up correctly, or put more than one image on a page when the finished size is less than the size of the press sheet.
Technical preflight may reveal problems with the file that will compromise quality or prevent raster image processing. It is our policy to complete technical preflight and report the results to you within 24 hours of receiving the file. We’ll let you know if the file passed preflight and has been scheduled for printing, or if we uncovered a problem. If there’s an easy fix, we’ll give you the cost of repair so you can approve, or you can ask to have the file returned so you can fix it yourself.
Please be aware that there are some problems that we consider “fatal flaws” that we’ll always ask that you repair before resubmitting the file. One example is an RGB color space when the file will be used for offset printing. This is because we want you to view the color after converting to CMYK or spot color to be sure it is acceptable. Other fatal flaws are lack of the one-eighth inch allowance for images that bleed and low.
resolution images. It is very helpful if when submitting a PDF file you let us know anything that intentionally deviates from standards, like a low-resolution, pixelated image included for artistic effect, so we will not count this as a fatal flaw.
Allowing for finishing operations
Some documents, like brochures or booklets, require additional work after printing that must be taken into account during file preparation. Here are the allowances for folding, drilling and booklet binding.
• Folding. To produce a completely flat and even fold, the size of panels that fold in must be slightly smaller. To compute the adjustment mathematically, determine the width of single panel if all were the same size, reduce the width of the panel that folds in by at least one-eighth inch (or more, depending on the thickness of the paper being used for the job), divide by two and add that amount to each of the outside panels. In addition, the position of the inside panel changes from the front to the reverse.
• Drilling. When the finished product requires holes, allowance needs to be made in the margins. We recommend a half inch clear space an 8.5 x 11 sheet, so shift the margin to the right for one-sided pages. For two-sided pages, shift right for odd-numbered and left for even-numbered pages.
• Booklet making. Booklets consisting of more than two or three flat press sheets folded into a booklet are subject to shingling – the effect of having each folded signature (i.e., multiple finished pages on a press sheet) wrapping around all previous signatures. After binding, the opposite edge is trimmed to produce an even edge. Without an allowance for this trim, it is possible that text, page numbers or other images may be trimmed away. Though paper thickness and the total number of signatures affect the allowance, you can use this rule of thumb when the booklet is 16 pages or less: subtract 1/32” from the face margin with each successive, interior signature. This means move everything 1/32” toward the gutter margin.
Unleash the power of PDF
We hope this discussion will help you prepare perfect print ready PDF files. If you find you have questions, give us a call at 781.337.0002 and we’ll do our best to clear way the confusion.