I noticed that this tool doesn't preserve links within PDFs. ( https://github.com/Hopding/pdf-lib/issues/341 ) That's one of the main things I always try out with PDF editors, and it saddens me to see that this one also runs into that issue.
Fixes would be either using a different PDF library, or manually implementing that feature with the building blocks that pdf-lib provides.
Not sure if you're referring to external or internal links but external ones are indeed preserved when once you download the modified PDF.
I've updated it so that external links are also clickable when viewing the PDF in the editor. Working on getting internal links to be clickable and function as well.
Let me know if this fits what you're after