ppi vs dpi etc (i've used ppi here since PS and many pdf exporters etc use the term ppi, ppi and dpi get used synonymously a lot – fine in most circumstances, but they are not actually the same), anyway:
Important note on illustrations and Word
Depends a bit on which version of word you have and how some advanced settings are set*, but as a general rule: do NOT only store your illustrations inside a word document, as word resamples images without asking. So your nice 300ppi print image would get made into 220ppi, eg lower quality. Always keep a copy of each illustration in a regular folder outside of the word document, in addition to any copies of it you have placed in it.
*file – options – advanced – image size and quality
Also on images
Consider using reverse image searches, tineye etc, to help you find author of anonymous illustrations?
Image resolution notes:
If you cannot find the image at 300ppi this is not the end of the world. Depending on the image it *may* still be possible to use the image as it can be resampled up to a higher res, or just printed smaller. That said ymmv greatly image to image with resampling, just because you make an image 300ppi, does not mean it will print well. Eg, if i take a tiny 72dpi thumbnail of a photo, enlarge it to be 100cm*100cm at 300ppi, it will still look awful printed that big, even though it says it is 300dpi.
(^i realise this is obvious, but might be worth mentioning for those not used to dealing with images, as what is written currently is very generalised.)
Should be plenty of ways to put links in .pdf s without the link printing differently.
AFK with real life, still checking PMs