Shrink Image Size
Most PDFs contain images. If your program has a PDF Optimizer, you will want to audit your space usage to determine what part of the file is causing the large file size of your PDF. You can reduce the size of images by finding the "downsampling" tool in your PDF program. Downsampling will reduce the resolution of your images. Be cautious that your level of downsampling does not completely distort your images. Whenever possible, use vector-based images instead of GIFs. Vector-based images require less file space. Consider using RGB instead of CMYK images. CMYK images present better color quality, but if you are more concerned with file size over color quality, RGB images are preferred.
The PDF Optimizer may tell you that your fonts are to blame for the file size of your PDF. Using multiple fonts will increase the file size. Review your document for font usage. The less fonts used, the smaller your file size will be. Your file size will also be reduced if you choose to un-embed fonts. When a user opens your file, their computer will select the font already installed on the computer. If their computer does not contain your chosen font, the computer will select a new font. This may change the look of the document. If you use an uncommon font, you will absolutely want the font embedded in your PDF.
Check the Level of Compression
Check the compression settings in your PDF program. This can reduce the file size of your PDF. When making changes to your PDF, select "Save As," and re-name or overwrite the file. Simply selecting "save" may increase the final file size. If you have made other changes, you may want to compare the two files. In this case, you will want to re-name the file, rather than overwrite it.