In DMS, For 1 candidate , different Credentials are generating for different companies.

Steps to be follow to execute this Issue:

step1: As a admin send document "X" to candidate A from company say "cbInternalBeta".
step2: As a admin send another document "Y" to same candidate A from different company say "stagingcbInternal".
step3: Candidate A will get both document "X and Y" on same email-id. 
step4: When candidate got mail for Registering on the particular company ,assumptions is Candidate will have same Username and Password from both companies.  But he is getting different Credentials.

Please have a look, it should have same credentials so that when Candidate logged into his candidate profile , he can see different companies in "company dropdown".