When I "place" a jpeg in InDesign, I can find out its PPI using the Links tab on the right hand side of the screen. However, when I place a pdf in InDesign, the ppi is not listed. How can I find out the ppi of pdf images placed in InDesign? I ask because I need to make sure the image quality is at least 300 ppi for printing purposes.
PDF files are not images. They are usually containers for a variety of objects—text, images of various resolutions and color spaces, and, for interactive PDFs, objects like video, sounds, or buttons.
To examine a PDF file you need to open it in Acrobat Pro. Use the Print Production tools, especially the Output Preview panel. In that panel, you can view the resolution(s), color space(s) and properties of objects in the PDF.