I don't think you can make .pdf files smaller.
Your options are to leave them as they are, or use JPG or GIF files, which will be smaller.
Are these documents, as in having text and images, as opposed to being just image files?
If so, PSE is not your axe of choice for this job. Do it in Preview. Open the file, choose File>Save As, choose PDF as the file type and then you will see a pulldown menu labelled Quartz filter. You can choose Reduce file size there. However, be aware that PDFs are likely to suffer a substantial decrease in quality when you do this, probably more than it's worth for the relatively small decrease in size.
If they are just image files, rescan them in an image format. It will be much easier to create smaller files from an image, without going the PDF route.
Thanks guys, I got it done, I did scan them as jpg files and didn't have anymore issues.
You could have used the option of quality slider present while using the email feature in Elements Organizer. This will automatically reduce the size of image.