Sarah BEWICK 

Sarah BEWICK said:

 Is it possible to imput a source document primarily in the target language with only elements in the source language to be translated

Of course... you can input whatever you like.

Sarah BEWICK said:

Is it possible to imput a source document primarily in the target language with only elements in the source language to be translated and can these elements be detected automatically?

Potentially this is possible using AnyTM, but you need to be careful as it's not foolproof.  This article might help:

https://multifarious.filkin.com/2014/02/12/supertm/

You didn't mention the version of Studio you are using but AnyTM is part of the product these days so the content of the article is useful I hope, but don't go to the appstore for it unless you are using a really old version of Studio.

If that doesn't work for you then your best option is to prepare the source file and hide all the text you don't want to be translated.