DEVONthink allows you to get a link to a selected page in a PDF document (Edit > Copy Page Link, hold ⇧Shift to show this open). Power user Chen Guo has created the open-source tool Excerptor that goes even further and links directly to selected text. Once installed, select some text in a PDF and choose Excerptor from the Services menu. Then paste the created link wherever you like to use it, e.g. into a rich text document. See this animated GIF for how it works.