PDFs, with particular font dictionaries, when placed into Adobe InDesign CS4 and exported to PDF, will result in some or all of their text not being drawn correctly when viewed in Acrobat 8.x or earlier versions, or rendered in an imaging system which uses the Adobe PDF Library version 8.x or earlier.
The fonts in the original PDF are embedded as symbolic fonts. Acrobat and PDF Library 8.x and earlier are not capable of correctly rendering symbolic fonts if the font encoding doesn't contain the glyph names for every glyph in the font.
This standard has a requirement for font encoding which prevents this issue from appearing in the resulting PDF when selected.
Note: This does not mean that you need to use the PDF/X-4 PDF Preset. You can use any settings, as long as the PDF/X-4 standard is also selected.