Elements 4 Slide Show PDF File Size

Question

My a 36-slide show with music ends up as a 6.76 MB PDF file. Are there techniques for reducing the file size?
My attempts have had mystifying results. I fould that 2 of the original images were multi-megabyte BMP files, so I replaced them one-by-one with much smaller JPGs, and made PDFs after each step. (Miraculously, when I edited the original photos, the edits automatically flowed down into the slide show images.)
When I made the replacements and created new PDFs, the size didn't shrink accordingly. It appears that Elements makes its own JPGs from the photos in the slide show, so the size of the original doesn't matter.
But replacing the first big file with a smaller one slightly INCREASED the size of the PDF, from 6.76 MB to 6.79. Replacing the second one increased it again from 6.79 to 6.80. Small changes, but mysterious.
BTW, taking out the music (built-in looping audio from Elements) reduced the file size from 6.76 to 5.87 MB.
Are there other ways to reduce the size of the PDF file?

Answer 1

Yep, I know this is user-to-user. I've gotten very good answers here, too.
I experimented with the "slide resolution" (or whatever the name of it is). There wasn't much difference in file size between 800x600 and 1024x768, and I couldn't see much difference on the screen. Fonts seemed less jazzy with 1024x768, but it wasn't night and day.
File size ballooned when I went to the next higher resolution. I think the visual quality improved, too, but I can't be sure.
Looks like the higer resolution settings might be good if one distributed the slide show on CD.