I was recently sent a PDF file where some of the metadata appeared to be wrong. In particular, the PRODUCER field was appearing in Chinese.
Oh dear, I thought (or slightly less poetic words to that effect), and opened the file in Acrobat to see where I had gone wrong. That is where it became interesting, because this is what Acrobat 9.0 showed.
I opened up the PDF file in a text editor to look at the data and here is the PDF information object
20 0 obj<<
/Producer(˛ˇScanSoft PDF Create! 5; modified using iText 2.1.7 by 1T3XT)
The Producer value is between 2 brackets and although it looks like a text string, it is in fact a binary values which can be encoded either as 2 byte unicode or as PDFDocEncoding (essentially ASCII so it actually looks like text in a viewer). The key to the mystery here is the 2 funny characters at the start ˛ˇ which are actually byte values 254 and 255. This indicates that the rest of the data is 2 byte Unicode. As you can see this is not the case.
So the problem is that the string is wrongly encoded. Some tools are either assuming it must be PDFDocEncoding (so getting it right in this case) or have their own strategy for spotting the mistake.
There are quite a few cases where PDF files can deviate from the Spec, such as the All TrueType Fonts are MAC encoded (unless they are not), issue I wrote about in another post.
Have you found any oddities in your PDF files?
This post is part of our “Understanding the PDF File Format” series. In each article, we discuss a PDF feature, bug, gotcha or tip. If you wish to learn more about PDF, we have 13 years worth of PDF knowledge and tips, so click here to visit our series index!
IDRsolutions develop a Java PDF library, a PDF forms to HTML5 converter, a PDF to HTML5 or SVG converter and a Java Image Library that doubles as an ImageIO replacement. On the blog our team post about anything interesting they learn about.