File - download

https://biuro.biall-net.pl/SE/version-git/wfs-data.php/default_db/?SERVICE=WFS
&VERSION=1.0.0
&REQUEST=GetFeatureAdvanced
&TYPENAME=p5_objects:File
&SRSNAME=EPSG:3003
&Filter=<ogc:Filter><ogc:PropertyIsEqualTo><ogc:PropertyName>id</ogc:PropertyName><ogc:Literal>35</ogc:Literal></ogc:Filter>

Result:

<?xml version="1.0" encoding="utf-8"?>
<wfs:FeatureCollection
    xmlns:wfs="http://www.opengis.net/wfs"
    xmlns="http://www.opengis.net/wfs"
    xmlns:gml="http://www.opengis.net/gml"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p5_objects="https://biuro.biall-net.pl/wfs/objects"
    xmlns:p5="https://biuro.biall-net.pl/wfs"
    xsi:schemaLocation="https://biuro.biall-net.pl/wfs/objects https://biuro.biall-net.pl/dev-pl/se-master/wfs-data.php/default_db/?SERVICE=WFS&amp;VERSION=1.0.0&amp;TYPENAME=p5_objects:File&amp;REQUEST=DescribeFeatureType">
    <gml:featureMember>
        <p5_objects:File fid="File.35">
            <p5_objects:id>35</p5_objects:id>
            <p5_objects:name>blank-test-wfs.gif</p5_objects:name>
            <p5_objects:size>64</p5_objects:size>
            <p5_objects:mimeType>image/gif</p5_objects:mimeType>
            <p5_objects:version>0</p5_objects:version>
            <p5_objects:content>R0lGODlhAQABAIAAAP///////yH+EUNyZWF0ZWQgd2l0aCBHSU1QACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==</p5_objects:content>
        </p5_objects:File>
    </gml:featureMember>
</wfs:FeatureCollection>