The most common issue that affects processing speed and can give unexpected print results is the use of layers and transparencies in PDF files. Transparency defines what happens when two or more objects overlap each other in a document. Transparency features are used extensively in Adobe Creative Suite® applications to apply special effects to objects, such as drop shadows, opacity and feathering. However, transparency may become an issue any time there are layers of objects in documents created with any application.
Understanding transparency issues requires an understanding of the flattening concept. During the processing of a PDF file for printing, the first thing that occurs is the 'flattening' of the document. (When printing directly from Acrobat, you can see a flattening status dialog.) Flattening takes all the layered, transparent objects on the page and converts them into opaque objects that look the same as the original transparent objects when printed. This flattening process can be quite time consuming depending on the complexity of the PDF file. Usually long processing time equates to complex transparencies being flattened. Sometimes the transparent objects are not flattened correctly and the resulting prints do not match the original document. This usually results in "blacked" out areas or missing data in the printed output.
Another common problem is missing fonts in PDF files. The fonts used in the original document should be included in the PDF file created from it. Sometimes the fonts are not included. This results in font substitution (i.e. wrong fonts) when printing.
Page boxes define the physical dimensions or size of the PDF file. There are five types of page boxes (MediaBox, BleedBox, CropBox, TrimBox and ArtBox) that can be defined in a PDF that describe its size. A PDF file may not print correctly or take a long time to process if these are not defined properly.
Most engineering and architectural drawings are created in color, even though they will be printed in black and white. It might be something as simple as color lines or a company logo. Or, there could be more complex color 3-D models or high resolution photos. This color information makes its way into the PDF files.
While more and more documents are being printed in color, many are still printed in back and white. There can be issues when color is converted to grayscale. For example, the color yellow might be very visible on a monitor but will become a very faint gray when printed in black and white. For on screen viewing, RGB color is appropriate. However color printers typically use CMYK inks or toners. Colors can change during this conversion process. The absence or presence of color in a PDF and how the color is defined can impact processing times and the final printed output.
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