How can I construct the HTTP call to upload DocX or PDF documents?

Hi,

I'm struggling to get the correct HTTP call. When I follow the API documentation the files are being uploaded as txt files instead of the correct file extension (DocX or PDF). I've read in another thread that base64 encoded wasn't supported, but the documentation still states that the stream is base64 encoded. But as this isn't working what kind of stream should I offer in the HTTP call to have a DocX or PDF correctly being uploaded?