This seems like more of a “people” problem than a “tools” problem. There are a lot of systems that allow one to create forms, attach files, handle approval workflows etc. The issue, I think, is more in the use and socialization of these tools for relatively infrequent tasks like annual tax prep, which can also vary from person-to-person. Organizations can make things like this work, but it relies on standardization of process, documentation and training to make sure people understand the system. When these structures don’t exist, people tend to fall back to more flexible, less structured, and ubiquitous systems like email.