I’ve to integrate the PDF in Ascii 64 on my XML external invoice - I’m on APP10 UPD17

On my transformer, i use this instruction :

1/ I dump on XP variable the 1st part of the file name, then i use concat to get the correct file name , in a variable named filepdf

<xsl:variable name="XP" select="invoiceId" />
<xsl:variable name="filepdf" select="concat($XP,'.txt')"/>
 

2 / On the XML tag <attachement> : i try to load the contain of the .txt file 

                   <ATTACHMENT>
                        <xsl:value-of select="unparsed-text($filepdf)"/>
                    </ATTACHMENT>
On message i get this error : 

Error while preparing input data. 
Caused by: ifs.fnd.base.SystemException: Transformer error: Error checking type of the expression 'funcall(unparsed-text, ivariable-ref(filepdf/string)])'. 
Caused by: javax.xml.transform.TransformerConfigurationException: Error checking type of the expression 'funcall(unparsed-text, kvariable-ref(filepdf/string)])'. 
Caused by: com.sun.org.apache.xalan.internal.xsltc.compiler.util.TypeCheckError: Error checking type of the expression 'funcall(unparsed-text, cvariable-ref(filepdf/string)])'.

I’ve tried to change version 1 to 2, on the header : but no more result

xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="urn:ifsworld-com:schemas:einvoice_service_receive_einvoice_request" version="2.0" exclude-result-prefixes="xs">