The current distribution of wkhtmltopdf in apt-get is not patched with latest version Qt,
hence there are many issues in wkhtmltopdf.
To solve this, we can manually install updated wkhtmltopdf from official website itself.
First, install from apt-get itself, (sudo) apt-get install wkhtmltopdf
Next, download the updated file from http://wkhtmltopdf.org/downloads.html
After extracking it, copy the binary from downloaded file, to the /usr/bin, (sudo) cp /bin/wkhtmltopdf /usr/bin/
I got these errors
QSslSocket: cannot resolve CRYPTO_num_locks QSslSocket: cannot resolve CRYPTO_set_id_callback QSslSocket: cannot resolve CRYPTO_set_locking_callback QSslSocket: cannot resolve sk_free QSslSocket: cannot resolve sk_num QSslSocket: cannot resolve sk_pop_free QSslSocket: cannot resolve sk_value QSslSocket: cannot resolve SSL_library_init QSslSocket: cannot resolve SSL_load_error_strings QSslSocket: cannot resolve SSLv3_client_method QSslSocket: cannot resolve SSLv23_client_method QSslSocket: cannot resolve SSLv3_server_method QSslSocket: cannot resolve SSLv23_server_method QSslSocket: cannot resolve X509_STORE_CTX_get_chain QSslSocket: cannot resolve OPENSSL_add_all_algorithms_noconf QSslSocket: cannot resolve OPENSSL_add_all_algorithms_conf QSslSocket: cannot resolve SSLeay QSslSocket: cannot call unresolved function CRYPTO_num_locks QSslSocket: cannot call unresolved function CRYPTO_set_id_callback QSslSocket: cannot call unresolved function CRYPTO_set_locking_callback QSslSocket: cannot call unresolved function SSL_library_init QSslSocket: cannot call unresolved function SSLv23_client_method QSslSocket: cannot call unresolved function sk_num
There is solution wkhtmltopdf/wkhtmltopdf#3001 (comment)