Open source LLM model for question answering

Hi, can anyone help me on building question answering model ? Or any other open source LLM with 1B parameters so that it can be executed in 4 GB GPU machine

I have my data in pdf, txt format (unstructured format) I want to build conversational question answering model. Could you please provide me any relevant article?

Like, how to build conversational question answering model using open source LLM from my data.