I don't know which program was used to create the PDF file, but I suspect it was MS Word. I was lucky in that the creator of the PDF had left it non-DRMed so I was able to use Adobe Acrobat Pro to fix the problem, though I don't really know what the problem was.

I'm no fan of PDF. Acrobat Pro does not allow you to select all the text in an entire document and change the font size. As a matter of fact, Acrobat Pro, which costs $500+, has very little editing capability. Like most Adobe programs it is overpriced and underfeatured. Converting a PDF to Word or another usable format is a lot of work because PDF files don't work the same as a DOC, RTF, HTML, ePub, etc. file when it comes to text flow. PDF files instead use text boxes and break up the text flow into a multitude of small chunks. It is a terrrible publishing system that was designed to reproduce a document in a specific size. It was never designed for reflow. In my opinion the time of PDFs has long since come and gone and this archaic system needs to be replaced or retired.