Can we delete a part from a hard disk if there is a lot of bad sectors and we can't make low level format for it ?i

It is a matter of check disk while on safe mode using command prompt to clean badsectors; a system repair and updated antivirus..

Using  some free ware software to fix bad sectors and then delete data from your hard drive otherwise use data sanitizing software to complete wipe the hard drive. Most reliable free ware data sanitizing software is DBAN (Darik Nuke and boot) to destroy everything from your hard drive.