Hello Shareef,
EditApprovable permission is required to edit a requisition. You can refer to ApprovableType.csv file located at Buyer\Server\config\variants\variant1\partitions\partition1\data folder. For each approvable document edit permissions are defined in the same file. There are some more details in the files like prefix to be used for an approvable (for insatance PR for requisition), number from which sequence starts, permission required to create or search an approvable document. It's quite an important file.
Thanks,
Amit