All the text of the journals is stored in a field and when you do a search this field is searched in all the journal issues.
So, if, for example, you searched on arbour – looking for articles by or about Ron Arbour you will get a lot of Journals returned (because there the address of Mike Frost is Arbour Close.
If you just type ron arbaor there will be matches on either ron or arbour
If you want to search on a phrase contain it in double quotes e.g. “ron arbour” and you should find Journals which have this phrase.
In the PDF viewer you can CTRL-f (or CMD-f) to show the find tool (in that PDF).
Hope this helps,