Hi Javed,
in the installer Advanced settings there is an option to run an executable after the installation. Batch files are allowed too; in the .bat file you can register ActiveX dll's by means of the regsvr32 utility.
For you second question: I know that an LV executable (exe) can be enabled as an ActiveX server by checking the proper option in the Builder's Application settings. The server has its own interface that you can't modify, but you can execute vi's, get/set data etc. But I'm not sure that you can use an LV dll as an in-process server into a (non-LV) ActiveX client.
Paolo
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LV 7.1, 2011, 2017, 2019, 2021