Merge multiple type (extension) files into one using C# and VB.Net in Console Application

I want to combine 2 or more files having different extension i.e. .txt, .pdf, .docx. to single file in Console Application.

Explain with example.

I want to merge WordFile (.docx), PDF(.pdf), Text File(.txt)

I want to copy only text available in these files to single file having .mrg extension.

Note: The text could be anything i.e. English words, Japanese, Hindi, Marathi.

Please help :)

Thanks in advance.