pdfpreview
I have 3 files about 40 KB each. When I combine them using Preview and save them as a single PDF file, instead of having a size close to 120 KB, the size is closer to 500 KB.
Why does this happen, and is there any way to retain a small file size when the files are combined?
I can't really answer as to why it's so inefficient, but i've had the same problem, and i got around it by using free Quartz filters from Jerome Colas.
This post on the Apple discussion boards has the details, but the link is broken, an extra * on the end breaks it, it should be https://public.me.com/jcolas.
Download, unzip, and add the "Filters" folder to your Library folder.
To use, open a PDF in Preview, click File > Save As, then select Quartz Filter, and the level of compression.
I believe that Jerome is exposing something that already exists in OSX, but certainly, it's a good solution that works well for me, allowing me to get a good balance between quality and filesize.
The size difference of a few hundred kilobytes can be attributed to the PDF version and encoding.
Recent versions of PDF introduced features to reduce the file size. These features included compressed object streams in v1.4.
A PDF file can look identical but be stored on disk in nearly infinitely different forms. The application responsible for creating the PDF is critical to getting the smallest possible file size.
Most applications, such as Preview, will call out to a general purpose PDF framework or library to deal with the file format. This will result in well formed files with minimal effort by the application's developers.
Other applications may create PDFs highly-tuned to their content and needs. The PDF specification allows for creative reuse of content, de-duplication, and optimisations that require knowledge of the document's purpose and intention. This requires significant effort and is increasingly rare.
Best Answer
PDFs are funny creatures because Postscript is a very "fat" language; the same PDF can be written multiple ways. I would say that the extra code is probably glue code to put those three documents together and extra bits placed there by whatever utility was used to combine the three.
The best way to get rid of this would be to open the PDF in Acrobat Professional (not Reader) and run it through the "Reduce File Size..." command. This strips out any dead or unnecessary code, optimizes fonts (if two instances of the same font exist, the PDF is rewritten so that only one instance exists), and the like.
Ghostscript probably has a function that does something similar, but off-hand I'm not sure which one that would be.