DRS - Entities Legal-API/Filer | Bug Fix

- [ ] Fix error when replacing file with certified copy
Resolve the error that occurs in the legal-api when attempting to replace memorandum and rules files with certified copies. The issue appears related to data format compatibility with the PyPDF2 library.
- [ ] Add unique validation on entity-filer/business-filer
Implement validation to prevent the creation of a new document record when a DRS record already exists for the given filing.
- [ ] update filing date once cont. in is completed

____________________

### **Doug Lovett Note 2026-05-21:**
I think this ticket is out of date but could be repurposed to capture the business filer changes when filing submission completes and the filing has one or more client documents. In this scenario the DRS record needs to be updated with the filing date and filing ID. If the filing creates a business identifier then the DRS record needs to be updated with this identifier as well. This work is outstanding.