There is no such file-level resolution-association in InDesign. The elements of your InDesign layout retain their respective characteristics; a 72 ppi raster image can live alongside a 300 ppi raster image and a 150 ppi raster image, as well as resolution-independent vector graphics and text; and they all remain exactly as they are, independent of each other with respect to resolution.
There is no resolution for an InDesign document. Raster resolution is controlled by the creating application.
Further to the above:
Vector files, such as .ai or .eps etc. have no resolution and output as they are.
Raster images, gif, png, tiff, jpg, psd etc. all can contain different resolutions within the document.
For each raster image you can select them and choose Window>Info to read the PPI within the images.
- Actuall PPI refers to the image at 100% and what resolution it is.
- Effective PPI refers to the image at the scaled size and the effects of the scaling has on it's PPI
For example, a 72 DPI image placed and scaled to 24% would yield a resolution of 300 ppi (72/24*100=300)
Placed PDFs can contain both raster and vector elements - that is a PDF file is a wrapper that can hold different elements
When you export to PDF from InDesign you can choose to reduce the PPI of images (say images over 350 ppi to be resampled to 300ppi) this means that an image that's 300ppi placed at 10% would effectively be 3000ppi - way too high for printing lithographically, so the option to downsample images on export to pdf is great way to save PDF size.
Exporting to PDF also allows you to control the colour conversion for web or print (rgb or cmyk), or no colour conversion at all (that is placed RGB and CMYK images remain this way) and how you want images downsampled etc. for printing or the web etc.
John Mensinger wrote:
.. The elements of your InDesign layout retain their respective characteristics; a 72 ppi raster image can live alongside a 300 ppi raster image and a 150 ppi raster image ..
It can even be 3 times the same image. The output resolution does not depend only on the input rez, but also to the image scale in the document. The actual value is indicated by the effective ppi value in the Info and Lonks panel.