Does it show on screen in ID in Preview mode?
If the answer for Peter's question is "yes", I suspect the following:
You export to PDF with the option "Export Layers: All Layers" and you have a layer set to "Show Layer" NOT checked in the Layer Options panel above your graphic with an object that obscures your vector graphic filled with the color of your background. Thus the image will be included in your exported PDF but effectively does not show.
If so, just export with "Export Layers: Visible & Printable Layers".
If this is NOT the case then we possibly could circumvent the problem:
Is your placed vector graphic of the file type EPS?
Do you have Acrobat Pro and Acrobat Distiller installed?
If so, try to convert that EPS to PDF using Distiller, preflight it with Acrobat Pro and place the PDF.
If the answer is "no" (you could not see your graphic in Preview mode), some of the following could apply:
1. The holding frame of the graphic OR the graphic inside the holding frame is marked as "Nonprinting" in the attributes palette (check both instances).
2. The object is positioned on a layer with "Print Layer" NOT checked in the Layer Options panel and you export with "Export Layers: Visible & Printable Layers" in your PDF export settings.
Another very common problem is a vector filled with white and set to overprint. This is nearly impossible to create natively in ID, but freakishly easy in Illustrator. White translates to no ink in ID and overprinting no ink does nothing.
Peter Spear wrote:
…filled with white and set to overprint. This is nearly impossible to create natively in ID…
Surprisingly it's very easy: fill a rectangle with a named color, set the fill of the rectangle to "Overprint Fill" in the Attributes panel, change the named color to white with all color values for Cyan, Magenta, Yellow and Black set to "0". The overprint attribute to the fill will stick.
Yes, editing an existing named color will work, but defining a color as white to start will not, nor will setting the overprint attribute with a color that will overpint applied, and changing the color to an originally defined white. This is in stark contrast to Illustrator where you never lose the overprint attribute unless you actually remove it manually.
And by the way, thanks for reminding me how to do it in ID. I spent about an hour once trying unsuccessfully to make a native white object overprint on a test file, even though I knew there should be a way (not that one should do it). That's why I said "nearly" impossible. It seems fairly unlikely in a normal workflow that users would re-define a named color to be white rather than using [Paper] or a new swatch defined as 0,0,0,0. Even defining a Spot White won't overprint in ID unless you first define it with some CMYK value, then edit to 0,0,0,0.