Hello,
I have extensive experience in .Net (C#), working in the software development industry for more than five years i have worked on developing complex applications in almost all areas e.g. Desktop apps, web apps, web services, WPF, WCF, Web API etc.
Here is how i plan to complete your task:
Step#1
Read the shap file in C# and convert it to a CSV file (i already have the code to convert shp file to a csv file)
Step#2
Dump the entire CSV in a local DB table as the data is huge. or alternatively loading a set of rows (e.g. 5000) at time in a .Net DataTable Class object.
Step#3
Start reading every single row and keep converting the co ordinates to Lat,Long and write to a new DB Table.
Step#4
Finally dump the final table in the CSV that you need.
Further discussion can be done on this in PM.
Thank You