<?xml version="1.0"?>

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  version="1.0">

  <xsl:output method = "text"/>

  <xsl:template match="Document">
    <xsl:apply-templates/>
    <xsl:value-of select="document('urn:arielpartners:propfolder/foo/properties')/Properties/NameValue[Name='who']/Value"/>
  </xsl:template>

</xsl:stylesheet>