No need to cross-post on SO as the posts are automatically brought over to the DevNet if they are tagged with "Kentico".
See the answer I provided, looks like a syntax error.
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{% if(!String.IsNullOrEmpty(Document)) { %}
<a target="_blank" href="~/getattachment/{% Document %}/attachment.aspx" download>{% DocumentText %</a> // your error is here, missing a closing curly brace after the percent sign for DocumentText
{% } else if (!String.IsNullOrEmpty(ExternalDocumentUrl)) { %}
<a target="_blank" href="{% ExternalDocumentUrl %}">{% DocumentText %}</a>
{% } #%}
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