Restoring a BACPAC isn't the same as restoring a SQL Server native backup (created using the
BACKUP DATABASE syntax).
A native backup using
BACKUP DATABASE is created by exporting all schema & data by backing up at the page level into backup files. By convention, these generally have a .bak file extension. A
RESTORE DATABASE does the inverse to create a database by copying the data pages out of the .bak and into the database. (It's a little more involved than this, but that's the big picture.) If the source database is encrypted with TDE, the data pages in the backup are also encrypted.
A BACPAC is created by generating
CREATE statements for all of the schema, then doing an export of data. The .bacpac file itself is actually just a zip file of the
CREATE scripts & data export. When doing a "restore" of the BACPAC, it simply executes the
CREATE scripts, then does an import of the data. If the source database is encrypted with TDE, the exported data within the .bacpac file is not encrypted.
If you want to create a TDE-encrypted database using a BACPAC, simply pre-create an empty database and enable TDE on that database. Then, import the BACPAC into that empty database, and Bob's your uncle.