declare 
    Dest_Clob  CLOB;
    Src_Clob   BFILE;
    Dst_Offset NUMBER;
    Src_Offset NUMBER;
    Lang_Ctx   NUMBER := Dbms_Lob.Default_Lang_Ctx;
    p_Warning  NUMBER;
  
    Len          NUMBER;
    l_Buffersize NUMBER := 3556437; 
    Amount       NUMBER;
  
  BEGIN
        delete clob_test;
        commit;
        Src_Clob := Bfilename('C_TEMP','TEST.xml');
        Dbms_Lob.Open(Src_Clob, Dbms_Lob.Lob_Readonly);
        Len := Dbms_Lob.Getlength(Src_Clob);      
        Dbms_Lob.Createtemporary(Dest_Clob, FALSE);
        Dst_Offset := 1;
        Src_Offset := 1;
          LOOP
            IF (Src_Offset + l_Buffersize - 1 > Len) THEN
              Amount := Len - Src_Offset + 1;
            ELSE
              Amount := l_Buffersize;
            END IF;
          
            Dbms_Lob.Loadclobfromfile(Dest_Lob     => Dest_Clob,
                                      Src_Bfile    => Src_Clob,
                                      Amount       => Amount,
                                      Dest_Offset  => Dst_Offset,
                                      Src_Offset   => Src_Offset,
                                      Bfile_Csid   => 873,
                                      Lang_Context => Lang_Ctx,
                                      Warning      => p_Warning);
          
            EXIT WHEN Src_Offset > Len;
          
          END LOOP;
          insert into clob_test(id,
                                i)
                                values(Dest_Clob,1);
          commit;
end;

select d.*
 from 
  CLOB_TEST a,
   Xmltable('//Файл/Документ' Passing Xmlparse(Document a.id) 
                Columns 
                IDDoc VARCHAR2(1000) Path '@ИдДок'
               )d
    WHERE       a.i=1;

declare ...

declare 
    Dest_Clob  CLOB;
    Src_Clob   BFILE;
    Dst_Offset NUMBER:=1;
    Src_Offset NUMBER:=1;
    Lang_Ctx   NUMBER := Dbms_Lob.Default_Lang_Ctx;
    p_Warning  NUMBER;  
  
  BEGIN
        delete clob_test;
        commit;
        Src_Clob := Bfilename('C_TEMP','TEST.xml');
        Dbms_Lob.Open(Src_Clob, Dbms_Lob.Lob_Readonly);
        Dbms_Lob.Createtemporary(Dest_Clob, FALSE);
        Dbms_Lob.Loadclobfromfile(Dest_Lob     => Dest_Clob,
                                      Src_Bfile    => Src_Clob,
                                      Amount       => Dbms_Lob.Getlength(Src_Clob),
                                      Dest_Offset  => Dst_Offset,
                                      Src_Offset   => Src_Offset,
                                      Bfile_Csid   => 873,
                                      Lang_Context => Lang_Ctx,
                                      Warning      => p_Warning);
          
      DBMS_LOB.CLOSE(Src_Clob);
      insert into clob_test(id,
                                i)
                                values(Dest_Clob,1);
          commit;
end;

with a as (select XMLTYPE(bfilename('C_TEMP','TEST.xml'),NLS_CHARSET_ID('AL32UTF8')) xm from dual)
select d.*
 from 
   a,
   Xmltable('//Файл/Документ' Passing a.xm 
                Columns 
                IDDoc VARCHAR2(1000) Path '@ИдДок'
               )d