There are a number of solutions to this problem published on YouTube, and memoQ Translation Technologies Ltd. (mQtech, the solution artists formerly known as "Kilgray") even has a nice help page in their knowledgebase, but all the solutions I have seen so far are either a bit dated, or they omit some information which might help to avoid problems.
The best free solution I have seen is the one described on the mQtech knowledgebase page, but the current description still leaves a few potential stumbling blocks.
There are two pieces to the solution:
- a conversion utility kindly provided by WordFast on the page https://www.wordfast.net/wiki/Translating_SDL_Trados_packages and available in the current version directly here, and
- a DLL that is needed in the same folder as that utility for it to function. Only the 32-bit version of sqlite3.dll on the page https://sqlite.org/download.html will work; the 64-bit version is useless in this case.