Question about document type vs _document type in c#

[awatt]

I'm working on an addin in c#, and am puzzled by intellisense telling me this:

(vairable invDoc is of type PartDocument)

The 2024 API help documentation gives the parameter type as only document.

Can someone give an explanation of the _Document type? A c# lesson may also be involved.

[Michael.Navara · Accepted solution]

The same question is answered here

https://forums.autodesk.com/t5/inventor-programming-ilogic/document-vs-document/td-p/3772072

[awatt]

Thank you.