Class behavior based on given data

I am receiving an IFormFile from a controller. What I want to do next is to process it and get its content. I expect to get .docx, .txt or .pdf file and I want a single class to process any of these files based on extension given. I created and made my class to do it like that:

{
    public static class DocumentProcessor // Should it be like this?
    {
        public static string GetContent(IFormFile file)
        {
            var result = new StringBuilder();

            switch (Path.GetExtension(file.FileName))
            {
                case ".txt":
                {
                    using(var reader = new StreamReader(file.OpenReadStream()))
                    {
                        while (reader.Peek() >= 0)
                            result.AppendLine(reader.ReadLine());
                    }
                    break;
                }
            }
            return result.ToString();
        }
    }
}

Anyway, I feel like it is an extremely bad solution just because it is static. I could use the strategy pattern, but how do I define what strategy context has to use? Should I create another class that returns a Strategy object depending on IFormFile object extension. But I feel it is also a bad solution I would like to know what is the best way to solve this problem