Android : open pdf using hmac

I traced the files created when browsing an e-Book (.pdf) using special ebook reader application installed on my android that i have bought an books from it

i try to download the pdf file to my computer it's ok downloaded but cannot open it it's given me white pages ..I'm not familiar with encryption pdf files.. but I'm looking for any way that i can open it since i have the hmac code here the responding i got it if i request to open the book the ebook reader received

<fulfillmentToken fulfillmentType="buy" xmlns="http://ns.adobe.com/adept">
    <distributor>urn:uuid:10344192-0619-4454-0003-206542567541</distributor>
    <operatorURL>http://example.com:8081/fulfillment</operatorURL> 
    <expiration>2015-03-21T20:46:10+02:00</expiration>
    <transaction>15-043567_54</transaction>
    <resourceItemInfo>
    <resource>urn:uuid:10344192-0619-4454-0003-206542567541</resource>
    <resourceItem>1</resourceItem>
    <metadata>
    <dc:title xmlns:dc="http://purl.org/dc/elements/1.1/">bla bla bla bla</dc:title>                                                                <dc:creator xmlns:dc="http://purl.org/dc/elements/1.1/">bla bla bla</dc:creator>                                        
    <dc:format xmlns:dc="http://purl.org/dc/elements/1.1/">application/pdf</dc:format>
    <dc:publisher xmlns:dc="http://purl.org/dc/elements/1.1/">bla bla</dc:publisher> <dc:description xmlns:dc="http://purl.org/dc/elements/1.1/">some description here.</dc:description>                     
    <dc:identifier xmlns:dc="http://purl.org/dc/elements/1.1/">ISBN:12345678</dc:identifier>  
    <thumbnailURL>http://example.com:8081/Thum/12345678.jpg</thumbnailURL>   
     </metadata>
    <src>http://example.com:8081/media/rbx_9953438358.pdf</src>     
     <downloadType>simple</downloadType>
    </resourceItemInfo>
    <hmac>0csdfAQOVJ01sdfsqRERGERSExA=</hmac>
</fulfillmentToken>