Can I send my own file, logo, text, or reference material?

In many cases, yes. In fact, for some categories of custom work that is exactly what makes the order possible. A custom logo object, a personalized GBbook, a custom print, or another tailored project may depend on the buyer providing a file, a source text, a visual reference, or at least a clear direction. But sending something does not automatically mean it is immediately usable in production. File quality, format, scale, clarity, copyright constraints, and the technical suitability of the source all matter. So yes, reference material can often be part of the process, but it should be understood as the start of a feasibility check, not as an automatic instruction that bypasses design or production reality.