How to import multiple textfile with different column into database using ssis?

If the same employees appear in all files then ignore files 1,2,3 and just get the data from file 4.

But assuming that different employees exist in each file then you could load up all of the files individually then add a step to combine them into the single table like this

select ename, sal, job, dept 
into tbl_emp
from file4 
union
select ename, sal, job, null from File3
union
select ename, sal, null, null from File2
union
select ename, null, null, null from File1

Add a final step to get rid of the "temporary" tables that you used for each file.

Note I started with the file that had all of the columns in it (File 4) rather than with File 1 - this means I didn't have to define a column type for the null columns when I was initially creating the table.
If the table tbl_emp already exists then it doesn't matter what the order is and you need to move the insert like this

insert into tbl_emp
select ename, sal, job, dept 
from file4 
union
select ename, sal, job, null from File3
union
select ename, sal, null, null from File2
union
select ename, null, null, null from File1