Ahhh PDFs…., or more formally, Portable Document Format files. I remember the days when I thought that PDFs were only for instruction manuals downloaded from the internet, or electronic copies of things that you don’t want people to be able to alter. Not so – I have recently discovered the joys of PDFs, particularly through my use of Mac OS X. I will explain more below:
1. PDFs are a vector filetype. That means that when there is text in a PDF document it is stored as text, with details of the font, size and location. When there is a line in a PDF document it is stored as a line from one location to another, with details of colour, width etc. This has a number of benefits – principally that PDFs maintain their quality no matter how much you zoom into them. You never get the horrible pixelated look that you can get with raster graphics files (such as JPEG and PNG). For scientific documents this is great – it means I can generate a graph, and then with one file I can produce an A3 sized copy for use in a poster and a 6″ x 4″ copy for inclusion in the paper. Not only that, but the 6″ x 4″ copy actually looks good – it looks professional, clean and high quality. Recently I had to include a PNG graph in a LaTeX document that I was writing – I hated it, all of the lines were blurry, I couldn’t resize it and it generally looked un-professional. Of course, I’m not suggesting you should store your holiday snaps as PDFs – that’s not what they’re designed for – but for diagrams, graphs and other technical drawings they are perfect.
2. PDFs are cross platform. Nearly every system can read PDFs these days. The standard is now open (ISO 32000-1). There are readers for Windows, Linux, OS X, Android, iOS, Palm, BSD, BeOS – you name it, it’ll probably have a PDF reader. Google Chrome even has a built-in reader these days – and many websites have stopped saying “This is a PDF file. If you don’t have a program to view them please download Adobe Reader”.
3. PDFs can be included in LaTeX documents extremely easily. Yes, I know you can include PNG files just as easily, and possibly it’s even easier to use PostScript files (although who doesn’t use PdfTex these days?). As mentioned above, raster files for graphs just look horrible, particularly when included in a LaTeX document in which (as is nearly always the case with LaTeX) all of the rest of the design and typography is near-perfect.
4. PDFs do not have to be A4 sized (or Letter, for those in the US). I know – I didn’t realise this until very recently, but you can crop PDFs to any size. In fact, there is a great perl script called pdfcrop which will crop a PDF file to the minimum bounding rectangle of the contents – taking your A4-sized PDF with a 6″ x 4″ graph in it down to a 6″ x 4″ PDF – perfect for inclusion in a LaTeX document, for example.
5. PDFs can be annotated easily. For example, as the text in a PDF document is stored as text, it can be selected just like text in a word processor, and then highlighted just as easily. Of course you can also add extra text or vector illustrations (such as circles around important features in a diagram). This is great for making notes on, and highlighting papers, articles and e-books.
6. PDFs are a first class filetype in OS X. I never knew how much I’d value this until I started using OS X. By default so many things are PDF. For example, PDF export is built into the standard OS X print dialog box. On Windows you’d have to install something like CutePDF to do that – but OS X does it by default. In fact, if you use the Print Preview function in the print dialog box, OS X simply prints to a PDF and shows you the PDF in the aptly-named Preview application. In fact, this application – which can display almost any graphical filetype – is also a powerful PDF editor. Using Preview you can re-order PDF pages, merge PDFs, annotate PDFs and crop PDFs. PDFs are a first class filetype in other ways too – all Spotlight searching by default searches within text in PDF files, and there is a separate section in the Spotlight dropdown for PDF files. Overall, Apple just seem to ‘get’ PDF.