You can read a PDF file (at least you can in newer formats) as though it were text. You will find an embedded XML section that uses the Adobe XMP schema. This contains the metadata you need.
Here is an example:
%PDF-1.5 %âãÏÓ 2 0 obj << /AcroForm 4 0 R /Lang (en-GB) /MarkInfo << /Marked true >> /Metadata 5 0 R /Pages 6 0 R /StructTreeRoot 7 0 R /Type /Catalog >> endobj 5 0 obj << /Length 2971 /Subtype /XML /Type /Metadata >> stream <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?> <x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.1.2"> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="" xmlns:xmp="http://ns.adobe.com/xap/1.0/"> <xmp:CreateDate>2014-03-05T15:03:02+01:00</xmp:CreateDate> <xmp:ModifyDate>2014-05-30T11:58:02+01:00</xmp:ModifyDate> <xmp:MetadataDate>2014-03-05T14:03:46Z</xmp:MetadataDate> </rdf:Description> <rdf:Description rdf:about="" xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"> <xmpMM:DocumentID>uuid:8b5fe011-ed77-4298-aa84-d1eda797b9ff</xmpMM:DocumentID> <xmpMM:InstanceID>uuid:88074e0b-42f7-4268-bc89-0162e417c9ad</xmpMM:InstanceID> </rdf:Description> <rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/"> <dc:format>application/pdf</dc:format> </rdf:Description> </rdf:RDF> </x:xmpmeta>
The following example will retrieve the create date:
$a = Select-String "CreateDate\>(.*)\<" .\filename.pdf
Which returns something like:
filename.pdf:20: <xap:CreateDate>2009-11-03T10:54:29Z</xap:CreateDate> filename.pdf:12921: <xap:CreateDate>2009-11-03T10:54:29Z</xap:CreateDate>
Getting to the exact data:
$a.Matches.Groups[1]
Which returns:
2009-11-03T10:54:29Z