XSL rendering a PDF in PDF

I am suffering with the issue of getting a local .pdf into my rendered PDF. I currently have a template for a picture where i can easily load images into my PDF.

<!-- Picture -->
    <xsl:template match="picture">
        <fo:block text-align="left">
            <fo:external-graphic src="url('file:///C:/Images/testImage.jpeg')" content-height="5cm" />
        </fo:block>
    </xsl:template>

I wonder if it is possible to get this done on the same way for a PDF. Currently i am unsuccessfully trying to use

xmlns:fox="http://xmlgraphics.apache.org/fop/extensions"

so what i have done looks like this:

<!-- Chart which is saved as PDF-->
    <xsl:template match="chart">
        <fo:block text-align="left">
            <fox:external-document content-type="pdf" src="url('file:///C:/Pdfs/ExampleChart.pdf')"/>
        </fo:block>
    </xsl:template>

I am using FOP 2.3 and the Error i get is

org.apache.fop.fo.flow.Block cannot be cast to org.apache.fop.fo.pagination.Root

So what i expect is that i cant use fox:external-document there but thats exatly the place where i need the PDF to be.

Thanks for your help!!!

Solution

Ok I think i just luckily found the solution i was looking for on my own! i Just added the jar files from: HERE to the lib directory of the FOP folder. Then i was able to embedd the PDF like so:

<!-- Chart -->
<xsl:template match="chart">
    <fo:block text-align="left">
        <fo:external-graphic src="url('file:///C:/Pdfs/ExampleChart.pdf')"/>
    </fo:block>
</xsl:template>

Hope this will help anyone who is suffering on the same problem :)