Hey @Ahsan_Mohamed
As per your user story just wants to make some changes, like below:
1.Get the outlook mails - 
2.Select the specific mail(specific mean search on mail subject) - can use "Filter mail property with Get outlook mail activity as well.
3.Double click the attechment (It’s a pdf file) - insted of this approach you can use either “Save Attachement” Activity with filter option or can check this post as well:
4.Enter the password for view the attechment- To view the pdf file use “Read pdf Text” activity and enter username and password to it’s properties.
5.Finaly I saved the the file at specific location in my machine.- No need because you have done this with step 3
Let me know, if you still have a doubt on this 
Regards…!!
Aksh