Email links are rewritten by Pardot and are uniquely tracked to their recipient. To ensure a proper link rewrite, you must not use spaces or special characters in your URLs. Anything included in the basic structure of the URL is ok to leave un-encoded, but anything after the basic URL structure (like a file name of a PDF) must be encoded.
Pardot will scan for spaces and apostrophes in <a href=””> tags and automatically replace them with their encoded equivalents (%20 and %27), and trim out newlines. Note that this only works for well formatted links in <a href=””> tags in HTML content. This cleaning only happens when an email is autosaved or you advance to the next stage in the wizard. HTML content imported to text will also be cleaned.
Even though Pardot will automatically encode spaces and apostrophes for you (only in well formatted links in <a href=””> tags), all other special characters in URLs must be encoded manually. You can use the following chart or this URL encoding tool.
Here are some common characters that require encoding.