Create file from MIME message

I want to create files from the attachments of a multipart mime message. I can retrieve the information I need and also the creation itself is not a problem. what I struggle is that with the given headers and bodies I am not sure what encoding should be used to create the files.

Let's say we have to attachments:

//HEADER    
Content-Type: application/pdf;
         name="somepdf.pdf"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
         filename="somepdf.pdf"
//BODY
 %PDF-1.4
    7 0 obj <</Length1 1501 /Length2 7274 /Length3 0 /Length 8281 /Filter /FlateDecode>>
    .. 
    ..


//HEADER
Content-Type: text/x-tex; charset=UTF-8;
     name="sometex.tex"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
     filename="sometex.tex"

//BODY
    \documentclass[a4paper, 12pt]{article}
    \usepackage[german,english]{babel}
    \usepackage{fullpage, graphicx}
    ..
    ..

If I want to create a file of this information how should I choose the encoding of the files? If I just take the body of the pdf e.g. and use it straight to write a pdf file it results in a not readable pdf, because the encoding is wrong. what is the correct encoding for the corresponding file? I am doing this on android with kotlin if you have some additional tips on how to do this