PDF file sizes, formats and filenames
What is a good PDF? Many people ask us this and the short answer is one that displays correctly and rapidly on your target platform(s) with your target software, e.g. Adobe or Javelin PDF readers. However, not surprisingly, there is more to creating a good PDF than meets the eye, and we are often asked for advice on how to produce optimized PDFs. Here are a number of tips that we hope publishers will find helpful:
PDF CREATION SOFTWARE: Use a really good tool for creating your PDFs – in general this means Adobe Acrobat/Adobe Distiller, but there are other options. OpenOffice has a Save as PDF option which creates very good PDFs although features such as bookmarking are not generated. For files created using older versions of MS Word, PDF Creator is an option that includes good detection of the headings structure in Word files and automatically creates all the navigation and hyperlinks you would expect to see. MS Office 2007 and 2010 have a Save as PDF facility which creates well-structured PDFs with contents navigation and and hyperlinks. However earlier versions can produce files that result in spurious lines around linked words and images when viewed on some earlier versions of the Mac OSX platform. In this case OSX needs to be upgraded or the file created using Adobe Acrobat X or a more recent version of MS Office, which generates the files correctly. Note that some freeware or low-cost PDF creation and editing software produces terrible files – for example, they may incorrectly encode images so that instead of a single image on a page it is fragmented into 10,000 bits – it may display OK in some PDF readers, but it may also take a very long time to appear on the screen!
PDF FILE SIZE: Use settings that are primarily targeted at screen usage rather than high resolution printing. Computer screens are nearly always less than 100dpi and tablet devices have relatively small screen although higher resolution, so select the “output for screen display” or “smallest file size” option in your software package (images downsized to 150-300dpi typically) – e.g. in InDesign or MS Office or Adobe Distiller printer. The result will be files that look absolutely fine and are much smaller – this means they download much faster for end users and open quickly and render on-screen well. Huge files are not a good idea – if you have a single file that is over 50Mbytes in size or 1000s of pages, think about creating it as a set of separate files, optimizing it for screen display, and if necessary, using a PDF Splitter program or Adobe Acrobat to split the PDF files into manageable chunks.
NAVIGATION: if your PDF has a structure but you do not provide a navigation tree and internal hyperlinks, it is much more difficult for your customers to find there way around the document. The Javelin readers are very good at supporting such navigation. If your PDF file does not have such facilities consider opening it in Adobe Acrobat and using the Add Bookmark facility to create a single level or multi-level navigation tree – this is very quick and easy to do, and improves the PDF considerably. You can also use this approach to create “folders” of multiple documents, with a cover page and navigation tree providing the index/links to the separate documents in the folder. When creating links on pages don’t use buttons as these are Adobe-specific form-related items and are not supported in Javelin (see below).
FILENAMES: keep filenames of the source PDFs short and simple, with no embedded spaces, hyphens or special characters. When securing a file with Drumlin it defaults the filename generated to be the same as the source PDF, with the extension .drmx or .drmz as appropriate. You can change the name of the drmx or drmz file and it will remain essentially unchanged – Javelin inspects the document’s internal ID to decide on whether it requires authorizing so the name you assign does not matter. Short filenames are easier for end users to download if they have to type them in, and are less prone to problems such as browser related issues when provided via web links. This also applies to the domain name for hosting – we have a number of short domain names and can host files for you at no extra cost – for example, drmz.net and pdfz.org and pdfds.com
TESTING: Always test the PDF you have created with the latest version of Javelin for each platform you are targeting – typically this will be PCs and Mac OSX computers, and possibly iPADs and Android tablets – it may also be aimed at phones, such as iPhones or Android phones, so think about their limitations in terms of size – most are less than 6inches/15cms, which is very small, so think about page sizes for such documents. Check the speed of display, the accuracy of font and special character rendering, image display and the navigation facilities (contents/bookmarks navigation trees and internal and external hyperlinks). You can test your PDF with Javelin prior to creating your DRMX or DRMZ files just by opening them in Javelin on the target platforms. Check also for any spurious lines that may appear – this is resolvable (see above for details)