I inserted a vector graphic in my Adobe Illustrator document:
Then I exported the Adobe Illustrator document to PDF, and opened the exported PDF in Adobe Acrobat Pro XI, where I saw that the vector graphic is not visible (screenshot taken as I was using the "Edit Text & Images" tool in Adobe Acrobat Pro XI):
This surprises me as I made sure that the image was at the front in Adobe Illustrator:
Yet in Adobe Acrobat Pro XI I had to bring to font to make the image appear:
I use Adobe Acrobat Pro XI and Adobe Illustrator CC 17.0.0 64-bit with Windows 7 SP1 x64 Ultimate.