A good (or maybe bad depending on how you look at it) example was an Edit document I was working on. I wanted to add parts of some images, and I was able to use Grab from the services menu to get the selected image into my Edit document (I don't have the license for TIFFany that I was using so this was the only way to save the image I was working on). Basically almost every OpenStep (later Yellow Box and then Cocoa) app provides a unique service to the other applications. It is quite cool.
That is a good question about pdf, and frankly I don't know. PostScript has been around sense at least the first LaserWriters came out (1985?), and people were using it as a document (and display) format by 1990. I didn't start getting really interested in pdf until Acrobat 3 (that was when the display quality started to match the print quality of pdf documents). Anything run on Acrobat Reader 2 or app based on it just didn't quite look right on the screen, but printed nicely. It is not hard to figure out why PostScript died out as a mainstream document format though, unlike pdf, there is no compression for images, so adding one simple picture to a document would make it massive (by early 90's standards). Today you can download pdf files without any secondary compression (I don't think I remember to many PostScript files on the web that hadn't been at least gzipped).
This does bring to light one of the major short-comings of the computer age. There doesn't seem to be a clear historical record of major technologies (other than maybe operating systems and hardware). I would bet that it is more by design than oversight. If people were able to easily find out were different ideas came from, Microsoft would lose it's place as an "innovator". Funny how when MIcrosoft jumps on the bandwagon, they crush everyone else that was there first (that produces quite the visual, don't you think?).