After seeing how big some of my previous PDFs have clocked in at, I've been experimenting with ways of cutting down file sizes for digital transfer and I thought a quick thread on optimising PDFs was in order. I appologise if I'm repeating anything that's gone before! Here are my tips for making useful PDF files anyway, and if anyone has their own tips feel free to chip in!
1) The big overhead in PDF file size is art. You can cut down how much space it takes up by lowering resolution and quality in your PDF driver's settings, but that results in a serious quality hit, especially if it's going to be printed out. Still, for complex colour artwork that's only meant for screen viewing not printing, it's the fastest method.
2) This is my favoured method of dealing with artwork. Take a vector-based drawing package (I use CorelDraw 10), convert your image to pure black and white (not greyscale, literally two colours) and trace it. Some vector drawing packages will do this automatically for you - mine does - though you may have to fiddle with the settings to get the perfect result. Not only does this mean that the results can be printed to any resolution without adjustment or quality loss, but it also results in a massive drop in file size overhead. For example, an image that was 175k in bitmap, and that at a resolution only fit to make it 3 inches wide at most, dropped to around 61k when converted to vectors even with simple cel-shaded colour added. This method works best on pure lineart however, and does require some work to neaten up the image. It doesn't require any great artistic talent though, and I think it's worth it. Adding the colour is easy too, as simple as tracing over existing lines.
3) Indexes and smart links are your friends. Don't neglect to convert everything you can find in the physical index into bookmarks as well as including that physical index for those who want to print it all off. Additionally don't forget that any page references (i.e. 'see page 15') can be converted into hot links that take you straight to that page. Changing the colour of the text in the screen version will drop the hint to the reader that this is possible.
4) Don't forget that a PDF's page numbering tends to differ from that of a printed copy. If your page 3 isn't on page 3 of the PDF, it's worth trying to adjust it a little so that it is. That way people can find the page they are looking for by skipping to it using the PDF reader's 'go to' option. You can adjust where the early pages are by adding blanks, moving the cover image to a separate file or putting in PDF-specific 'how to use this PDF' pages.
5) Print friendly versions are win. If you've got any colour or complex images at all, you should make one. Remove ALL art, especially repetitive page borders, or replace it with simple line-art versions with NO large areas of black whatsoever. If your screen display version is an odd size or shape, it's worth reformatting the whole document to fit US Letter Size. I use Letter rather than A4 because I feel that auto-resizing Letter to A4 for UK printing gives a nicer result than resizing A4 to Letter for US printing. Also the US is the larger market.
6) An obvious one, but don't forget to zip it all up when you're done.
7) Include, include, include those fonts. Not all fonts are capable of being included in a PDF file, so check very carefully to make sure they are. Adobe Acrobat has a special page for checking PDF inclusion compatability, but if you have another program then uninstall all common fonts from your system after making the file and then open it to make certain that it's working alright. Note that it's worth including the common fonts as well, since there may be slight variations between systems even in fonts with the same name.
8) I find that you get far better PDF compression sizes when using a dedicated layout package that supports PDF natively than just by using a generic PDF creator. I use Quark, which gives excellent size reductions. You may find it more difficult to get your vector images to import into such packages as vectors, but don't be tempted to convert them to bitmaps or you'll lose that size compression. Instead, see if you can import them as PDF files, and save them as PDFs from your vector package. This should also help you get text to wrap snugly around your images.
Ash
