Thank you for your post!
I tested the http://www.mbsplugins.eu/component_DynaPDF.shtml in a New Post and a reply to the post. They lead to the proper page. "https://community.filemaker.com/external-link.jspa?url=" is just how the community handles embedding the link into text. If you don't want the text/link to change you can remove the link by highlighting and clicking the icon below. In what way is this affecting you?
The link to my page in your post also got the community prefix. That is not needed and should removed.