Your Plan Documents will need to be signed by a representative of your company who is authorized to implement such a plan. Once the plan Documents are signed, they will need to be retained for your records. If you have received a new set of plan documents, but you have not made any changes to them (beyond the new plan year), you do not need to sign them.
The Plan Documents do not need to be sent back to Ameriflex. Your payroll provider may request to see them as confirmation that you do have a Section 125 plan in place. In the event that your are audited by the IRS, they will request to see these documents as well.