I'm not very good at XSL myself, but does this get you what you need?

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:a="test_3">

<xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>

<xsl:template match="/">

<xsl:copy><xsl:apply-templates select="/a:Report/a:Document"/></xsl:copy>

</xsl:template>

<xsl:template match="*">

<xsl:element name="{local-name(.)}">

<xsl:apply-templates/>

</xsl:element>

</xsl:template>

</xsl:stylesheet>