Read Document Error & Skipping Over Errors

I get the following error from the Read Document operator (inside Loop Examples after Read Excel with the input URLs).  It stops after successully reading several hundred records.  I have a log that tells me where the process stops, but do not see anything obviously wrong with the input URL.

Any thoughts on the possible cause?  And is there a way to skip past any troublesome input URLs rather than stopping the process with no output?

<?xml version="1.0" encoding="UTF-8"?><process version="7.3.000">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="7.3.000" expanded="true" name="Process">
    <process expanded="true">
      <operator activated="true" class="read_excel" compatibility="7.3.000" expanded="true" height="68" name="Read Excel" width="90" x="45" y="34">
        <parameter key="excel_file" value="/Users/carl/Documents/SD PDFs.xlsx"/>
        <parameter key="imported_cell_range" value="A"/>
        <parameter key="first_row_as_names" value="false"/>
        <list key="annotations">
          <parameter key="0" value="Name"/>
        </list>
        <parameter key="locale" value="English (United Kingdom)"/>
        <list key="data_set_meta_data_information">
          <parameter key="0" value="SvceDef Link.true.file_path.attribute"/>
        </list>
      </operator>
      <operator activated="true" class="loop_examples" compatibility="7.3.000" expanded="true" height="103" name="Loop Examples" width="90" x="179" y="34">
        <process expanded="true">
          <operator activated="true" class="extract_macro" compatibility="7.3.000" expanded="true" height="68" name="Extract Macro" width="90" x="45" y="136">
            <parameter key="macro" value="GetURL"/>
            <parameter key="macro_type" value="data_value"/>
            <parameter key="attribute_name" value="SvceDef Link"/>
            <parameter key="example_index" value="%{example}"/>
            <list key="additional_macros"/>
          </operator>
          <operator activated="true" class="log" compatibility="7.3.000" expanded="true" height="82" name="Log" width="90" x="179" y="136">
            <parameter key="filename" value="/Users/carl/Documents/Log.log"/>
            <list key="log">
              <parameter key="Log" value="operator.Extract Macro.value.applycount"/>
            </list>
          </operator>
          <operator activated="true" class="open_file" compatibility="7.3.000" expanded="true" height="68" name="Open File" width="90" x="246" y="34">
            <parameter key="resource_type" value="URL"/>
            <parameter key="url" value="%{GetURL}"/>
          </operator>
          <operator activated="true" class="text:read_document" compatibility="7.3.000" expanded="true" height="68" name="Read Document" width="90" x="380" y="34">
            <parameter key="content_type" value="pdf"/>
            <parameter key="encoding" value="UTF-8"/>
          </operator>
          <operator activated="true" class="text:extract_information" compatibility="7.3.000" expanded="true" height="68" name="Extract Information" width="90" x="514" y="34">
            <parameter key="query_type" value="Regular Expression"/>
            <list key="string_machting_queries"/>
            <list key="regular_expression_queries">
              <parameter key="Ark" value="[Cc]rown [Hh]osting|Ark Data Cent[re|er]s?|Cody Park|[sS]kyscape|Spring Park"/>
              <parameter key="Mainframe" value="Mm]ainframe"/>
            </list>
            <list key="regular_region_queries"/>
            <list key="xpath_queries"/>
            <list key="namespaces"/>
            <list key="index_queries"/>
            <list key="jsonpath_queries"/>
          </operator>
          <operator activated="true" class="text:documents_to_data" compatibility="7.3.000" expanded="true" height="82" name="Documents to Data" width="90" x="648" y="34">
            <parameter key="text_attribute" value="OriginalText"/>
          </operator>
          <operator activated="true" class="generate_attributes" compatibility="7.3.000" expanded="true" height="82" name="Generate Attributes" width="90" x="782" y="34">
            <list key="function_descriptions">
              <parameter key="URL" value="%{GetURL}"/>
            </list>
          </operator>
          <connect from_port="example set" to_op="Extract Macro" to_port="example set"/>
          <connect from_op="Extract Macro" from_port="example set" to_op="Log" to_port="through 1"/>
          <connect from_op="Open File" from_port="file" to_op="Read Document" to_port="file"/>
          <connect from_op="Read Document" from_port="output" to_op="Extract Information" to_port="document"/>
          <connect from_op="Extract Information" from_port="document" to_op="Documents to Data" to_port="documents 1"/>
          <connect from_op="Documents to Data" from_port="example set" to_op="Generate Attributes" to_port="example set input"/>
          <connect from_op="Generate Attributes" from_port="example set output" to_port="output 1"/>
          <portSpacing port="source_example set" spacing="0"/>
          <portSpacing port="sink_example set" spacing="0"/>
          <portSpacing port="sink_output 1" spacing="0"/>
          <portSpacing port="sink_output 2" spacing="0"/>
        </process>
      </operator>
      <operator activated="true" class="append" compatibility="7.3.000" expanded="true" height="82" name="Append" width="90" x="313" y="34"/>
      <operator activated="true" class="select_attributes" compatibility="7.3.000" expanded="true" height="82" name="Select Attributes" width="90" x="447" y="34">
        <parameter key="attribute_filter_type" value="subset"/>
        <parameter key="attribute" value="Text"/>
        <parameter key="attributes" value="URL|Ark|Mainframe"/>
      </operator>
      <operator activated="true" class="filter_examples" compatibility="7.3.000" expanded="true" height="103" name="Filter Examples" width="90" x="581" y="34">
        <list key="filters_list">
          <parameter key="filters_entry_key" value="Ark.is_not_missing."/>
          <parameter key="filters_entry_key" value="Mainframe.is_not_missing."/>
        </list>
        <parameter key="filters_logic_and" value="false"/>
      </operator>
      <operator activated="true" class="order_attributes" compatibility="7.3.000" expanded="true" height="82" name="Reorder Attributes" width="90" x="715" y="34">
        <parameter key="attribute_ordering" value="URL|Mainframe|Ark"/>
      </operator>
      <operator activated="true" class="write_excel" compatibility="7.3.000" expanded="true" height="82" name="Write Excel" width="90" x="849" y="34">
        <parameter key="excel_file" value="/Users/carl/Documents/Service Definition Matches.xlsx"/>
      </operator>
      <connect from_port="input 1" to_op="Read Excel" to_port="file"/>
      <connect from_op="Read Excel" from_port="output" to_op="Loop Examples" to_port="example set"/>
      <connect from_op="Loop Examples" from_port="output 1" to_op="Append" to_port="example set 1"/>
      <connect from_op="Append" from_port="merged set" to_op="Select Attributes" to_port="example set input"/>
      <connect from_op="Select Attributes" from_port="example set output" to_op="Filter Examples" to_port="example set input"/>
      <connect from_op="Filter Examples" from_port="example set output" to_op="Reorder Attributes" to_port="example set input"/>
      <connect from_op="Reorder Attributes" from_port="example set output" to_op="Write Excel" to_port="input"/>
      <connect from_op="Write Excel" from_port="through" to_port="result 1"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="source_input 2" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
      <portSpacing port="sink_result 2" spacing="0"/>