Can you buy an adapter to convert 35mm jack to spdif?

No, you cannot directly convert a 3.5mm jack (analog audio) to SPDIF (digital audio) using a simple adapter, as they are fundamentally different types of signals. However, you can use a digital audio converter that takes an analog signal from a 3.5mm jack and converts it to a digital SPDIF signal. This typically involves more than just an adapter, as it requires a digital-to-analog converter (DAC) or an audio interface with the appropriate conversion capabilities.