When you apply for a Cambodia visa, you will need to present the following documents:
Your passport, which must be valid for at least another six months and with at least one blank visa page
A return-trip ticket.
Cash in US dollars to pay the visa fee (US$30 for tourist visa; US$35 for ordinary visa)
When applying at an Embassy: Any other documents that the immigration officers require, such as a cover letter, invitation letter, etc.
Your passport format photograph.
After you arrive in Cambodia, you will need additional documents to extend your ordinary visa, depending on the type of extension you need, such as a work contract, proof of enrollment in a Cambodian school, etc.