When inserting/creating a hyperlink in a PDF document the link text is invisible

That's how Links in PDF files work. They don't have text as a part of them. You're supposed to place them over text that already exists in the file.

Alternatively, you can use a button field instead of a Link object. Then you will be able to set its caption (or label) to the text of the link, and add to it a Mouse Up action to launch it.