MKV and Adobe Revisited
All of this comes down to the fact that Adobe is a very oldfashioned company who simply refuses to support Matroska even though everyone knows it's the best video container out there.
But if you insist on using PrPro instead of a free tool, you gotta work around this issue. No reason to blame your brother. He is just using the best end user container format for lossless video there is. MP4 is primitive in comparison, and any other format is even worse due to all too many content restrictions and technical limitations.
Here's a workaround:
Use the freeware tool Avidemux to extract the H.264 AVC video stream from the MKV container.
Hopefully Premiere Pro will let you import that H.264 video file. Edit it and export it as a video stream again afterwards.
Then remux the H.264 stream with MKVmerge (also free). Open the original MKV file in MKVmerge and replace the old video stream with your edited version.
That way you may be able to preserve the advanced indexing and multiple audio+subtitle tracks in the Matroska file.
Good luck.
