A former employee of the Newton assessor’s office, accused of wrongly giving elderly residents a $1,000 property tax exemption,was arraigned Monday on charges of forgery and filing of a false report by a public worker. Stanley Dobies, 62, pleaded not guilty to the charges, said Stephanie Guyotte, a spokeswoman for the Middlesex County District Attorney’s office. If convicted, Dobies faces up to 10 years in prison, Guyotte said.