I am using :
qt version->4.8.7
Wkhtmltopdf version->0.12.5
And Microsoft visual studio 2015 So which version of openssl would be compatible with the above mentioned versions
That version of Qt has reached end of life a long time ago.
If memory serves well that was around the time of OpenSSL 1.0 which has reached end of life as well so it would not be recommended to use as of now.