Simply use the SoftMails OST to PST Converter software to convert OST files to PST. It can also import OST files to PST and many other 10+ formats including emails, documents, tasks, notes, chats, contact, calendar, attachments, deleted files, etc. It will give you many helpful features like Multiple naming options, bulk conversion, recovering damaged OST files, etc. you can enable to see the complete live preview of OST files items. It can never make any alteration in the structure or formatting of data.