When you create a PDF file that contains many images and multiple pages, the file size can become unmanageable. You cannot email a very large PDF file, even if you compress it, as many common email systems will only allow you to add files that are anywhere between 5 to 20 megabytes. The solution is to reduce the size of the PDF file yourself.
In Your Original Program
First, work with the images in your original program to reduce the size of your PDF file. Many PDF files are created in Microsoft Office (Word, Excel or PowerPoint), or desktop publishing programs. If your PDF document is coming out too large, it is most likely due to the images that you have inserted into the original file. Open all of the images in Adobe Photoshop and reduce the resolution by at least 100 dpi (dots per inch). If you don't own Photoshop, you can use GIMP, which is a free photo-editing program. For instance, if your images are 300 dpi, you can reduce them to 200 dpi or less.
Then go in and update the file that you want to turn into a PDF with the new images. Depending on the number of images in your file, this could save you multiple megabytes of space. Play with the images until you get the file to your desired size.
Keep in mind that if the PDF file will be printed, you don't want to reduce the resolution of the images by too much, or they could look pixelated on paper.
Reduce the File in the Adobe Acrobat Program
You can also reduce your PDF file size in Adobe Acrobat. Go to "Advanced" on your Acrobat menu and then select "PDF Optimizer." Click the "Audit Space Usage" button. You will be given a breakdown of what is taking up so much space in your document—the problem will most likely be your images. You can then "downsample" all of the images in your document using the PDF Optimizer. So for instance, you can ask the system to reduce all images that have a resolution over 600 dpi to 300 dpi automatically. Once the update is complete, you will be able to save the file as normal. Compare the new file size with the previous size.
Use "Create PDF"
The online PDF creation tool at CreatePDF.adobe.com also gives you the option to reduce the size of your PDF document. When converting your document, play with the "Job Options." Click "Convert a File" and find the file that you want to convert. You have two options for creating a smaller PDF file than usual. For one, you can either select "Web" or "Screen" from the drop-down box under "Conversion Settings." These produce smaller files that will only be looked at on-screen.
You can also select "Preferences" under "Set Options" and then click "Edit Settings" next to the box labeled "Optimization Settings." Choose a profile (Web, screen, print or other). On the next screen, you can reduce the resolution of your PDF output, or downsample your images as you would in the full Adobe Acrobat program.