I created links in an existing PDF using Adobe Acrobat Pro 8. I attached the PDF to an email. I opened the email in Gmail on my iPhone 5s. I tapped on the PDF to preview it. When I tap a link, I get a screen that offers 3 options: Open, Copy and Add to Reading List.
None of these work.
The links work perfectly on a laptop, whether in Gmail preview or when opened with the current Adobe Reader DC.
I subscribe to Creative Cloud, so have access to those Adobe products.
My original document is created in Word 2003, and I save it as a .prn file, and open that in Adobe Acrobat 8 and create the links there.