The same to last year, the SDK is now available at ADN Open . You can also download it directly from the link below:
AutoCAD_Mechanical_2015_SDK.exe (exe - 6427Kb)
The SDK contains libraries, header files, documentation, and samples for AutoCAD Mechanical APIs, which provide object-oriented C++ programming interfaces for developers to use, customize, and extend AutoCAD Mechanical software. Please refer to the readme for changes to this release of SDK.
The Developer’s Guide and ActiveX and VBA Reference Guide are also available:
acmdevguide_19_0.chm (chm - 208Kb)
acadmauto_19_0.chm (chm - 3972Kb)