src/fop-conf.xml

<fop version="1.0">

    <base>./</base>

    <font-base>./</font-base>

    <renderers>
        <renderer mime="application/pdf">
            <fonts>
                <directory>fonts/deja-vu-sans-mono</directory>
                <directory>fonts/nimbus-roman-no-9-l</directory>
                <directory>fonts/nimbus-sans-l</directory>
            </fonts>
        </renderer>
    </renderers>

</fop>