Websites use graphics to enhance information, assist navigation, and generally improve the user’s experience. To create those graphics, developers use any number of programs, like the Adobe Creative Suite (Photoshop and Flash have their own topics), the CorelDraw suite, Xara, Gimp, ACDSee, Serif, ULead and others.
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What application did you create the PDF in. If it was Adobe Acrobat Pro then you can open the PDF and the click "Save Other" and choose Reduced size PDF. If that isn't the application then I would need to know specifically what PDF application created the file.