Serve PDFs with correct Mime Type / Content Type

Hi - Is it possible to have imageresizing.net library serve non image files with the original content type?

I found this https://stackoverflow.com/questions/30273451/cache-xml-files-without-application-octet-stream-type/30309550#30309550
(but we have disk caching disabled so I dont know if applies here)

If it makes any difference we're using s3reader2 plugin

Here is the relevant packages.config:
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Start with the package configuration in the issue, especially ImageResizer, S3Reader2, and Storage, and reproduce how a PDF response is served. Trace where the response content type is selected and compare it with the original file type. Done means non-image files such as PDFs are served with their original content type rather than application/octet-stream.

Written by the indexing model from the issue text.