What kind of links do you use?
Links created in Acrobat are always relative (unless you hard-coded the file-path into a script or something like that). Move the file to another location and you'll see that they change accordingly.
When I looked at the links to the other document in the file as a ‘link to web or document’ it seemed to link to the file absolutely. Ie. File: C://docments/XYZ. When I changed the folder it updated the location so it was not a static link as I thought previously.
When I updated the pdf document in Illustrator it opens automatically into Adobe Acrobat DC. I tried to create the links from that window and the links didn’t work when I sent them to the client. If I opened them from the file directly it created the relative links that I needed to pass on but it didn’t show that way. They still looked like absolute links but they change depending on the file as long as both files are in the same folder. So I have it working now.
It was my method of linking that created the broken links see my reply to Bernd. The links appeared to be absolute in the dialog box but when I moved everything to a different folder the link updated. My web education made me think they were absolute but they are really relative which makes my life a lot simpler. Thanks for your reply!