SQL> -- I believe you need to place your call to the createPDFTable between BEGIN and END,
SQL> -- instead of using EXEC, when creating your strSql.
SQL> -- I also believe you need to use a callable statement and doLoad.
SQL> -- When testing, it also helps if you use the same parameters in SQL*Plus and Java.
SQL> -- Please see the example below.  I did not test your connection and exceptions.
SQL> --
SQL> CREATE TABLE PDFTable
  2    (directory_name VARCHAR2 (30) NOT NULL,
  3  	directory_path VARCHAR2 (30) NOT NULL,
  4  	table_name     VARCHAR2 (30) NOT NULL,
  5  	file_name      VARCHAR2 (30) NOT NULL,
  6  	source_bfile   BFILE)
  7  /

Table created.

SQL> CREATE OR REPLACE PROCEDURE createPDFTable
  2    (p_dirName   IN VARCHAR2,
  3  	p_dirPath   IN VARCHAR2,
  4  	p_tableName IN VARCHAR2,
  5  	p_fileName  IN VARCHAR2)
  6  AS
  7    v_src	       BFILE;
  8    v_dirPath       VARCHAR2 (30);
  9  BEGIN
 10    v_dirPath := UPPER (p_dirPath);
 11    v_src	 := BFILENAME (v_dirPath, p_fileName);
 12    INSERT INTO PDFTable
 13  	 (directory_name, directory_path, table_name, file_name, source_bfile)
 14    VALUES
 15  	 (p_dirName, v_dirPath, p_tableName, p_fileName, v_src);
 16  END createPDFTable;
 17  /

Procedure created.

SQL> SHOW ERRORS
No errors.
SQL> create or replace and compile java source named problem as
  2  import java.awt.*;
  3  import javax.swing.*;
  4  import javax.swing.event.*;
  5  import java.awt.event.*;
  6  import java.sql.*;
  7  import javax.swing.table.AbstractTableModel;
  8  import javax.swing.filechooser.*;
  9  import java.io.File;
 10  import java.io.InputStream;
 11  import java.io.*;
 12  import java.lang.*;
 13  import oracle.sql.*;
 14  import oracle.jdbc.*;
 15  public class problem
 16  {
 17  	public static void doLoad() throws Exception
 18  	{
 19  	   try
 20  	   {
 21  	      Connection conn = null;
 22  	      Class.forName("oracle.jdbc.driver.OracleDriver");
 23  	      conn = new OracleDriver().defaultConnection();
 24  
 25  	      String dirName  = "TMP_DIR";
 26  	      String pathName = "C:\courses\cs601";
 27  	      String opTable  = "emp";
 28  	      String fileName = "S5.pdf";
 29  	      System.out.println(pathName);
 30  	      String strSql   = "BEGIN createPDFTable ("
 31  			      + "'" + dirName  + "',"
 32  			      + "'" + pathName + "',"
 33  			      + "'" + opTable  + "',"
 34  			      + "'" + fileName + "'"
 35  			      + "); END;";
 36  	      System.out.println (strSql);
 37  
 38  	      CallableStatement stmt = conn.prepareCall(strSql);
 39  	      boolean xx = stmt.execute();
 40  	      stmt.close();
 41  	   }
 42  	   catch (ClassNotFoundException e)
 43  	   {
 44  	      e.printStackTrace();
 45  	      System.err.print("ClassNotFoundException: ");
 46  	      System.err.println(e.getMessage());
 47  	   }
 48  	   catch (SQLException ex)
 49  	   {
 50  	      String errMessage="";
 51  	      System.out.println("n--- SQLException caught ---n");
 52  	      while (ex != null)
 53  	      {
 54  		 errMessage=errMessage+" "+ex.getMessage();
 55  		 System.out.println("Message: "+ ex.getMessage ());
 56  		 System.out.println("SQLState: " + ex.getSQLState ());
 57  		 System.out.println("ErrorCode: " + ex.getErrorCode ());
 58  		 ex = ex.getNextException();
 59  		 System.out.println("");
 60  	      } // end while
 61  	   }
 62  	   catch (Exception e)
 63  	   {
 64  	      e.printStackTrace();
 65  	   } // end catch
 66  	} // end doLoad
 67  } // end problem class
 68  /

Java created.

SQL> SHOW ERRORS
No errors.
SQL> CREATE OR REPLACE PROCEDURE test_problem
  2  AS
  3    language java name 'problem.doLoad() ';
  4  /

Procedure created.

SQL> SHOW ERRORS
No errors.
SQL> SET SERVEROUTPUT ON
SQL> EXEC DBMS_JAVA.SET_OUTPUT (1000000)

PL/SQL procedure successfully completed.

SQL> EXEC test_problem
C:coursescs601                                                                
BEGIN createPDFTable ('TMP_DIR','C:coursescs601','emp','S5.pdf'); END;        

PL/SQL procedure successfully completed.

SQL> SELECT COUNT (*) FROM PDFTable
  2  /

  COUNT(*)                                                                      
----------                                                                      
         1