Now a days PDF is universally accepted as a most compact format for document conversion and transmission. However excessive use of images and fonts in a PDF result in its size increase. This leads to various problems like bounced e-mail attachments, unnecessarily long downloads, and higher-than-necessary internet bills. Hence size of a PDF should be reduced as much as possible. Balancing quality and file size in PDFs is quite tricky.
PDF size increases mainly due to three main reasons: images, fonts, and the PDF format itself. Images cause the main trouble. Many programmes (like keynote for example) embed them at much higher resolutions than you'd ever actually display which results in increase in file size. If you reduce these images you can save a lot of space. Fonts also can add bulk size. When standard fonts are used then there is very little need to embed them in the file and if nonstandard fonts are used, you can embed only the characters you use, rather than the entire font. Also if you do a lot of editing and page replacement in Adobe Acrobat, the size of your file will definitely grow every time you save. Thus how to reduce your PDF document depends largely on what tool you are using and how much control you want to exert over the process. Following are few measures to reduce the PDF size:
Use the Save As Command
When you make changes to your PDF, select (Save As) to overwrite the entire PDF. If you just select (SAVE), changes are added to your file resulting in size rise.
Manage your graphics
Always use vector-based graphics whenever possible. Vector-based graphics scale perfectly, look better and take up less space that helps to reduce your PDF.
Manage Your Color
If you are not much concerned about printing colours while making a PDF, use RGB colour space instead of CMYK which helps to reduce your PDF to a large scale.
If possible don't embed your fonts as fonts take up lot of space. However if it is compulsory try to keep minimum number of fonts.
Thus by following above procedures we can get a reduced PDF.