Catalog对象（根对象）
https://www.cnblogs.com/wlstm/p/11152142.html
我的文档：
obj
<</AcroForm <</Fields []>>/Metadata 3 0 R/Pages 4 0 R/Type /Catalog>>
endobj
3 0 obj
<</Length 633/Subtype /XML/Type /Metadata>>
stream
<?xpacket begin="锘? id="W5M0MpCehiHzreSzNTczkc9d"?><x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.4-c005 78.147326, 2012/08/23-13:03:03">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:xmp="http://ns.adobe.com/xap/1.0/" xmlns:pdf="http://ns.adobe.com/pdf/1.3/" xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/" xmlns:pdfx="http://ns.adobe.com/pdfx/1.3/" rdf:about="">
<dc:format>application/pdf</dc:format>
<pdfx:SWConverInfo>16</pdfx:SWConverInfo>
</rdf:Description>
</rdf:RDF>
</x:xmpmeta><?xpacket end="w"?>
endstream
endobj
4 0 obj
<</Count 3/Kids [5 0 R 12 0 R 14 0 R]/Type /Pages>>
endobj
2 0 obj
<</Author (?D
/ModDate (?
endobj
第二个对象 作者 文档 生产者