How can i process PDF using OpenAI (GPTs)?

In my UI i am allowing user to upload their resume in pdf or docx format then passing file to GPT-4 so it can review the resume and provide some tips to improve my resume,
this task is becoming more challenging as i wanted to achieve this by using C# lang using Asp.Net MVC framework

You might want to look into Azure Document Intelligence: it can take a pdf or docx and convert it into markdown content that GPT can then process.