The best way to convert OST to PST without Outlook is only possible by using the professional method and to execute this process you need to use the professional tool like Data Recovery Freeware OST to PST converter. But, why I'm recommending this tool so the reasons are;

- It converts the OST file into multiple file format like PST, DOC, DOCX, HTML, PDF, MHTML, etc. 

- This tool maintains the data hierarchy throughout the conversion process. 

- It maintains the data hierarchy through out the conversion process.

- It transfer the OST file to the number of email clients like Office 365, Thunderbird, Yahoo mail, Gmail, etc.

- This tool converts the OST file in bulk.

- It is compatible with the all the versions of Outlook and windows. 

Steps to convert OST to PST professionally

- Download and install the OST to PST converter.

- Then select the OST file to convert.

- Now select the OST file or folder to preview.

- Then select the OST file to convert and set the path to save the resultant file. 

- Lastly click on the convert button to start the conversion process. 

If you want to convert OST to PST in by using the different methods then read this article 03 Easy Methods to convert OST to PST in Outlook.