One of the special features of PRC (Product Representation Compact), as a modern best-practice method to embed 3D scenes in an interactive PDF View, is to add annotations and dimensional layers as special options.
Normally the full 3D model can be rotated, scaled and positioned in a 3D view for review, taking advantage of the PRC high compression features. Each view can optionally reveal other hidden information such as part labels, dimensional arrows lead lines and measurements or full PMI annotations.
If the model comes from one of the many 3D formats that does not include PMI or dimensional information, then PDF3D Conversion can specify “Automatic PMI”, where model dimensions are computed directly from the 3D shapes and dimension annotations are added, along with part specific views to reveal each annotation individually or in groups. On PDF3D ReportGen, it’s a simple check box feature.
If you already know you want specific labels and lead-lines at certain places on your model, then an alternative is to merge an annotation file along with the main conversion. For instance, if you have an STL or DWG file, a small additional VRML which can specify some text labels in just a few lines can be merged. Such small files can easily be edited by hand (samples are provided as a starting point) or scripted by some other system.
If you already have a PRC file (.prc) then this can be loaded, converted into a new PRC or 3D PDF containing the PRC model, with the addition of Automatic PMI or merged annotations from any other file format which supports text labels.
So CAD to PRC, PRC to PRC, and many other possible conversion pathways could be used to add rich annotations and dimensional layers to PRC based 3D PDF files.