Rewriting the output of a file download field I have a content type with two fields, one pdf field which will be downloaded using the Download File module which provides a formatter (file download) to automatically download the pdf file with one click and one image field linked to the pdf field, using the Linked Field module. This works in the node without problems. 
The problem is when trying to rewrite the results of the image field in Views.
I set the file field with the "File download fomatter" and exclude it from display.
Then, I try to rewrite results of the image field like this

&lt;a href="{{ file_download_field | striptags}}"&gt;{{ image_field }}&lt;/a&gt;


or

&lt;a href="{{ file_download_field.url }}"&gt;{{ image_field }}&lt;/a&gt;


but this is not working. 

The files are stored in the folder

[root]/file-download/download/public[node:field_file_download:entity:fid]


What am I missing?
The "File download fomatter" you're using doesn't output just the path to the file, it's a more complex formatter and you can't use it in your case as a path to download the file. 

In Drupal 8 there is a separate Field in File Views called URI that you need to use. 



Depending on which Drupal 8 version you're using you'll see only the formatter File URI and you need to tick the option Display the file download URI to get the link you can use in an anchor href attribute later when overriding fields. 

Do not enable Link this field to the file download URL, this outputs complex anchor HTML, not just the path that you're after. 

You can exclude it from display, position it above the image field and Rewrite results for the image: 

&lt;a href="{{ uri }}"&gt;{{ image_field }}&lt;/a&gt;

or let Drupal link it: