Print to PDF: won't open in Adobe Reader, but will in Preview

Subject says it all.
I use "Save as PDF" from an application and the resulting file does not open/display properly using Adobe Acrobat, but it opens and displays just great using Preview.
Dubya-tee-eff ?
Here is the offending PDF


What kind of file is produced directly, before using Save as PDF in the Printer dialogue?
I am not certain I understand the question. This app prints calendars. I hope to use the print-driver's "Save to PDF" feature to produce PDF's. The app prints. The options in the print dialog determine if it goes to the printer or the disc.
What should I know about Qt, as to why one would use it -- is this development related?
The Norway-trolls say it better than I can
Qt is a comprehensive development framework that includes an extensive array of features, capabilities and tools that enable development of high-performance, cross-platform rich-client and server-side applications.
Qt is the leading framework for native cross-platform application development. The Qt API and tools are consistent across all supported platforms, enabling developers to learn one API and perform truly platform-independent application development and deployment. Using Qt, development teams can create native applications for all major operating systems - from all major development platforms.