13 March 2014
Yes, son can file his father's income tax return as legal representative and son shall has to sign on return form and the details of son means name of son,father's name of sign and pan number of son has to mention at the signature place and has to fill the details of son at the representative option in the ITR form.
In case the return is filling manually then the death certificate of father has to be enclose along with the return form for A.Y 2013-14.
You said father has died in the month of July 2013 means father also have income upto July 2013 means have income for A.Y 2014-15 also so son has to file A.Y 2014-15 return of his father also after March 2014.
13 March 2014
In case if you filing such returns through e-filing then intimate to your Area AO by the Son about the his father death and last returns filed along with enclosures of death certificate, e-filed acknowledgements for A.Y 2013-14 and 2014-15 after completion of filing of A.Y 2014-15 return also.
In case if the father didn't have any taxable income upto July 2013 means for A.Y 2014-15 then after filing of A.Y 2013-14 return of income do the above process i said with the additional enclosure of Statement of total income of the father for A.Y 2014-15.