Is it possible to convert primary partition into extended?
No. This is a restriction in the (DOS) partition table structure – nothing to do with Linux. I would doubt that PM does it either – especially if you have the partition table fully populated with primaries. I presume you have “run out” of partitions, and want to create an extended so you can use logical partitions. You cannot use an extended partition to directly address your data. Using normal access anyway. If you have 4 primary partitions, you will have to delete one so you can create an extended (there can only be one on a disk). This is true even if you have unallocated space on the drive. Within the extended “container” you can define logical partitions that you can restore you data to.
