if i buy a psd template from themeforest , can I convert psd to html for themeforest html template?
Not without permission from the original author
How can I understand who gave permission to use the template ?
You need to contact with PSD Author.
You have to take full rights or html rights for convert psd to html form the original author
The author would need to:
give you permission (preferably in email/writing)
they may ask for an extended license or other agreement
they should open a ticket with envato support stating that you have permission to develop the PSD in another format and share the ticket ID with you