List entries of documents in a section grouped by checkbox
Your assets variable is defined outside the entries loop so it is still referring to the page entry. If you move it inside the loop it should work as expected.

{% set entries = craft.entries.section('documentLibrary') %}
{% for entry in entries if entry.documentType.contains('Report') %}
    {% for asset in entry.documents %}
       &lt;a href="{{ asset.url }}" type="application/pdf;" class="list-group-item active"&gt;{{ entry.title }}&lt;/a&gt;
    {% endfor %}
{% endfor %}


Rather than doing this manually however, you might also have a look at the group filter, which can group the entries array by document type.

{% set entries = craft.entries.section('documentLibrary').find() %}
{% set groupedEntries = entries|group('documentType') %}

{% for type, entriesByType in groupedEntries %}
    &lt;h2&gt;{{ type }}&lt;/h2&gt;
    &lt;ul&gt;
        {% for entry in entriesByType %}
            {% for asset in entry.documents %}
                &lt;a href="{{ asset.url }}" type="application/pdf;" class="list-group-item active"&gt;{{ entry.title }}&lt;/a&gt;
            {% endfor %}
        {% endfor %}
    &lt;/ul&gt;
{% endfor %}


Note: Also if each 'document' only contain one and only one 'asset' (i.e. pdf), then you can also get rid of the asset loop and just use {{ entry.document.first.url }}.