Application-level multi-tenancy is an increasingly prominent architectural pattern in Software-as-a-Service (SaaS) applications that enables multiple tenants (customers) to share common application functionality and resources among each other. This has the disadvantage that multi-tenant applications are often limited in terms of customizability: one application should fit the needs of all customers.In this paper, we present our experiences with developing a multi-tenant SaaS document processing system using current state-of-practice workflow technologies from the JBoss family. We specifically focus on the customizability w.r.t. the different tenant-specific requirements, and the manageability of the tenant-specific customizations.Our main experiences are threefold: (i) we were insufficiently able to modularize the activities and compositions that constitute the document processing workflow, (ii) we lacked support for describing tenant-level variations independently, and (iii) the workflow engine we employed is too centralized in terms of control, which limits resilience and thereby endangers scalability of the document processing application.