I work with Illustrator all day at a label factory and I think I have the answers for you. When saving to a PDF, only the image that is showing within the document area is going to show on your pdf. If your image is 2 feet x 4 feet (for example) and your document size is 8.5 x 11, then you will only see the portion that happens to line up within the document border. If you save as an .ai file or an .eps file, then all of the image, regardless of the document size, will show when the file is opened or placed. To make sure that the document can be opened without font problems, outline the fonts. This is done on a PC by holding down the control key, shift key and the "o" key at the same time. On the Mac, replace the control key with the apple key. Be sure to select all the copy that you want to outline first. As a rule, I do a select all, then outline the fonts and then I save as an eps file. This works best for almost all applications.
If you wish to save as an pdf file, make sure that your document size is large enough for all of the copy to fit into. Then do a select all and then outline all the fonts. Now when the file is opened into Illustrator there will not be any font issues. The file will not be able to be edited after you outline the fonts, so save the file before and after with different names. I usually save the file first as an .ai file with the fonts that are editable. Then I do a select all and outline the fonts and save as an .eps file. If I need to edit the file at a later date, I open the ai file. If I need to output the file, or send out the file, then I open or send the eps file.
I have noticed that almost never do you have a font problem when opening a file in Adobe Reader. But, opening a PDF file in Illustrator often requests fonts if they are not on your system. If a customer sends me a file that is not outlined and I have missing fonts, I do not ask for the fonts. I ask them to outline the fonts. This is not only a lot easier, but it keeps you from installing many fonts on your system that are not legal. For best results, you may forward to a service bureau (for output of signs, printing, labels, etc) an Illustrator eps file with the fonts outlined and a pdf with the fonts outlined also. This will insure that they can use the file and that the fonts will be correct. I have come across a few PDF files that when opened in Adobe Reader, have wrong fonts. This can be a real big problem as spacing may be different resulting in errors. Be sure to outline the fonts. Hope this helps. Sorry about all the details, but usually a little extra information can be dealt with easier than not enough.