How to return a PDF file from custom module?

Hi all,
I’ve a method of a custom module that should read a pdf file in the private file system (private://adir/226/fincav.pdf) and then return the file.
I can get the file data in this way:
$file = file_load($ifid);

and, given the file URI, that I know, I should read the file and return it as pdf download.

How can I do this?

Claudio

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