As an experiment, take a copy of this file or a copy of this layout and change the fonts to some other font. Does the text now appear?
This may be indicative of a problem with a font or font suitcase on this specific machine.
could it be the default font setting on the iMac?
I'm not currently a Mac User. I've just seen a number of reports here where a duplicate or damaged font suitcase resulted in blank layouts when the text in that layout was a font from the damaged font suitcase. Changing fonts made the text visible on the layout and replacing the damaged font suitcase with a new copy or removing the duplicate copy fixed the issue according to the reports posted back to the forum.
Problem solved ~~ On the iMac in question, the Arial font folder was missing from the Font Book. This is the font I was using on the "blank" PDF file. The fix:
1) from Finder, open Applications > Font Book.app, select "All Fonts"
2) File > Add Fonts
-------->> on another computer, export the Arial font folder in the Font Book and email it to the problem iMac. Drag the attached font folder to the Desktop <<----------
3) from the add-font window, select the Arial font folder from the Desktop and then click "Open"
As PhilModJunk suggested, I changed fonts on the problematic layout from which the PDF was being generated. I used a font I knew was in the iMac Font Book - this solved the blank-font problem. Since Arial is a font widely used in my FileMaker application, I wanted to fix the iMac rather than change to a different font on dozens of layouts.