Would you please explain what you mean by "cannot open a link"? Nothing happens when you tap the hyperlink? Is the hyperlink visible when the PDF document is opened in Acrobat Reader for iPhone and iPad?
What kind of hyperlinks do you have in the PDF document?
Acrobat Reader for iPhone and iPad supports the first two types of hyperlinks, but not the third one.
In contrast, the desktop version of Acrobat Reader supports all hyperlinks.