This cannot be done out of the box. The only alternative will be to
create your own upload page in ASP.NET and handle it this way

If you give me more detail, I will be happy to guide you in the right
direction

I am going to try my best to explain since
I am not really good at it. I created custom  document library  (list)
with some custom columns. I want to create another drop down column
like an asp one with all current employee names (textfield) and their
login ids (datafield). Later by click on the employee name based on
their login id I want to open an employee detail page. All employee
data are stored in the database. I am not fluent in calm so I was
wondering if I can insert some code to open and pool data  from the
database instead of hard coding chooses.

The information contained in this E-mail message is privileged, confidential,
and may be protected from disclosure; please be aware that any other use,
printing, copying, disclosure or dissemination of this communication may be
subject to legal restriction or sanction. If you think that you have received
this E-mail message in error, please reply to the sender.

This E-mail message and any attachments have been scanned for viruses and are
believed to be free of any virus or other defect that might affect any computer
system into which it is received and opened. However, it is the responsibility
of the recipient to ensure that it is virus free and no responsibility is
accepted by Kelley Drye & Warren LLP for any loss or damage arising in any way
from its use.

The closest way to achieve this is to create a list called Employees in
the same site and use a Lookup field  in the document  Library. If your
employee list is being maintained then you can use a way to copy the
data and paste into the document library

For a custom  solution, you will need to write a ASP.NET page to handle
the upload process.