My PC was slow so I formatted my local disc C. after that I cannot reinstall microsoft office.

[Jyothi96]

I have formatted my local disc C. Afer that I cannot reinstall microsoft office. some extentions are missing. I had microsoft office pre installed.

[TheOldMan]

If you had been registered at the Microsoft site for the Microsoft Office, then they will allow you a download to fix/repair the Office install. 

https://account.microsoft.com/account/Account?refd=support.microsoft.com&ru=https%3A%2F%2Faccount.mi...

If you cannot signin, then most likely need to find the product key and get it that way.

[Jyothi96]

Actually, microsoft was preinstalled in my PC, I had it installed  during the purchase itself. i contacted microsoft and they tried to fix my problem but they told that some extention files are missing so I should contact HP and ask for my hard disk information and the office as well 

[TheOldMan]

I am pretty sure that HP support does not have any info about the Microsoft Office software other than to sell it with the PC's.  If you know which version of Office was installed, you can reload the software with a new download.  That would be as if you did not have it preinstalled.

It is curious what "extension files" are missing, but HP does not have "Hard disk information" except the type and size of the drive when the PC was new. 1 TB 5400 rpm SATA

If there are any files missing, then it might depend on what was used to reinstall Windows 10.  You will still need the Microsoft Office download to reinstall and the product key.