MDF file full - cannot find the source of its giant size
Identify the top 10 biggest tables/indexes with this as a starter:

SELECT TOP (10) s.name, o.name, ps.row_count,
  used_bytes = ps.used_page_count * 8192,
  reserved_bytes = ps.reserved_page_count * 8192 
FROM sys.dm_db_partition_stats AS ps 
INNER JOIN sys.objects AS o
ON ps.[object_id] = o.[object_id]
INNER JOIN sys.schemas AS s
ON o.[schema_id] = s.[schema_id]
WHERE o.is_ms_shipped = 0
ORDER BY reserved_page_count DESC;


SQL Server doesn't just occupy 87 GB for nothing - the space is being used somewhere. Maybe it's in a system table:

SELECT TOP (10) s.name, o.name, ps.row_count,
  used_bytes = ps.used_page_count * 8192,
  reserved_bytes = ps.reserved_page_count * 8192 
FROM sys.dm_db_partition_stats AS ps 
INNER JOIN sys.all_objects AS o -- change this to all_objects
ON ps.[object_id] = o.[object_id]
INNER JOIN sys.schemas AS s
ON o.[schema_id] = s.[schema_id]
-- WHERE o.is_ms_shipped = 0 -- comment this out
ORDER BY reserved_page_count DESC;


Would also be curious to see what size the backup is, and what happens if you try shrink the data file.