The PDF format

Take some time to learn the history and details of the format with which you will be working. It helps to explain some of the the quirks you will meet along the way.
BIG WRITING – PDF is a ‘portable’ document format, able to be read anywhere there is a reader for it – WinMacLinuxAndroidUnixiOSBrowser. While it IS possible to change text or images inside a file (which was for years the basis of pre-press, changing a low-res preview at print time to a high-res copy) it is not, repeat is not a word processing format.
While, for many, the PDF format has been identified with Adobe, it is now an ISO standard (32000-1 for those who are interested). Anyone with access to the specification can make software to read a PDF file made by anyone else who may have created an original a completely different way. Get it here if you are really interested.
And now you are about to start making your own. From scratch.

Just one thing to grasp

A PDF is a dictionary of instructions and resources describing exactly HOW to recreate the document on whatever device or ecosphere you are using.
That in itself is at the heart of why you will find this method of working just so fast. On occasions all you will need to do is change the value in a dictionary location (and for the geeks among you these are all held as name value pairs) rather than render the document first and then re-save using something like a printer driver to work out where everything is on the page.

History

This is a really good article outlining the development of PDF at prepressure.com – from it’s original introduction in 1991 PDF as an internal Adobe project to us downloading invoices from all our web purchases.

John Warnock wrote: ‘Imagine being able to send full text and graphics documents over electronic networks. These documents could be viewed on any machine and printed locally. This capability would truly change the way information is managed’

More things to know

We ‘read’ from top down, left to right in most cases.
The co-ordinates inside a PDF are similar to a graph. The origin is bottom left and we read across then up. Units are 72dpi as PDF started life closely related to PostScript (users units are possible – but that might be lesson 47!) so something with a position of [144, 720] is two inches from the left of the document and 10 inches up from the bottom.
Oh, and what you see might not be all of the document either! As PDF is heavily used in high-end print there may be invisible constraints on what you see:

  • MediaBox – used to specify the width and height of the page
  • CropBox – the region to which the page contents is clipped. Acrobat uses this size for screen display and printing
  • BleedBox – the region to which the page contents needs to be clipped when output in a production environment. Usually 3 to 5 millimetres larger than the TrimBox
  • TrimBox – the intended dimensions of the finished page
  • ArtBox – can define a region within a page of special interest. e.g. allows you to place a PDF on another page but only use the ad from that PDF

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