To be clear, this document was not released by Trump.

This REDACTED SUMMARY version was declassified in 2014. See here.
What Trump has done is delivered a UNREDACTED FULL version of the report to a DC federal court to comply with a legal request.

The issues is that accusations were circulating that Trump’s administration would attempt to hide this report or prevent it from reaching the current trials of Guantanamo Bay detainees (in support of their defense). Instead Trump administration complied and delivered the requested report after dely by Obama administration.
President Trump Quietly Releases Documents No One Saw Coming and It’s Bad!………

h/t Tom