Once you are enrolled in your 401(k) Plan, you typically do not need to fill out paperwork unless you are making a change to your deferral rate. Otherwise, your contributions will continue to flow into your 401(k) account and your investment allocation that you originally chose. For many plans you can make changes to your deferral rate and investment election on-line or by telephone. However, there are still a number of plans that require paperwork be filled out to make these changes. You should contact your plan administrator-recordkeeper to explore these issues. The number or website address is always located on your quarterly statement. If you don't have a statement, go ahead and contact your HR or Benefits department.
I am not sure I understand the question. However here is a scenario. If you have money in a 401(k) plan and you have left the employment of that company the money will just sit there. Normally nothing happens to it unless you request distribution paperwork. Some retirement plans automatically cash you out and send you a check if the balance is less than $5,000.00. If you think you may have money left in a plan somewhere and are not sure who to call you can try the company's HR department or you can also check if your state has any unclaimed funds division if that company has moved changed hands or etc.. I hope that helps. If it doesn't please clarify the question.
Please be more specific. Are you currently enrolled in a 401K plan? Are you seeking to make amendments to your contribution amount? Are you trying to make withdrawals? To what documents (paper) are you referring?