No PDF app showing equations properly I have a PDF of a Ph.D. thesis in mechanical engineering, so there are lots of equations. No PDF app that I've tried on OS X (Preview.app,Adobe Reader, Skim, PDFPen) can show the equations properly; some symbols are missing (particularly integral signs). However, when I open the file in Windows (with PDF X-Change) the equations all appear right.

I don't know how the file was generated. Any idea of the cause of this issue?
Though Adobe Acrobat (and Adobe Reader) is the official standard tool for displaying PDFs, there are a variety of third-party tools that could have been used to create a given PDF. Though the output from such third-party tools can be passable, the underlying construction of the page layout can vary wildly.

Using Adobe Acrobat, it is possible to use [Cmd + d] to view the document properties, including what tool was used to generate the PDF. I'm not certain if Adobe Reader has the same functionality.