The file formats for translation memories that you can export from Trados and import into Déjà Vu are TMX and Trados WorkBench(txt). If you wish to import a Trados Translation Memory (including the SDLTM format) into Déjà Vu you must first convert the TM to one of these two formats.
You can read this article to find out how to convert your SDLTM files to TMX.
After that, you can import the resulting translation memory into Déjà Vu:
And how do I convert SDLTM into tmx?
Trados Studio should allow you to convert an SDLTM to TMX format.
If I had Studio, I wouldn't need to convert in the first place, but would use Trados for SDLPPX packages.
There is a resource called Trados Studio Resource Converter: http://vannellen.com/fortranslators.php
We have not tested this tool ourselves, but some of our users speak well of it. You can download it from here: http://vannellen.com/TradosStudioResourceConverter_2017-06-12.zip
Thank you, Lorenzo. For some reason I could not get Van Nellen's tool going on my computer, but the WfConverter did the trick in the end.
Best wishes,
Annika