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Embedded graphics in some PDFs in some readers on some computers may appear to be of poor quality, or be aliasedthey . However, this is likely an issue with the software settings in the PDF reader being used. To address this issue in Adobe Reader follow these instructions:
In Reader, go to Edit -> Preferences -> Page Display. Uncheck use 2D graphics acceleration, then you can uncheck smooth images, smooth line art, smooth images, enhance thin lines (if available).
Regardless, the PDFs will look great when printed. Almost all PDF files will be vector format so that users may zoom to infinity without seeing pixels.