I don't see anything seriously wrong with your Paph, though it does look a little stressed. A good picture of the whole plant, especially showing any new growth, would be more helpful than the dark blurry close-ups.
Older leaves eventually die back, and once they start there isn't anything that can stop it. As long as the yellowing leaf is the bottom leaf on an older mature fan of leaves, and newer growth is healthy, it isn't necessarily a sign of any serious problem.
The plant does perhaps look like it has been through dry conditions, low humidity, maybe a little too long between watering. You didn't say anything about the care you give, humidity, light, water quality, fertilizer. Some info would be helpful.
One thing I can say for sure... Anytime a Paph isn't doing well you should un-pot it to check the health of the roots, and it would probably be a good idea to repot it with fresh potting mix. Most Paphs should be repotted at least once a year, usually spring is ideal, but better sooner rather than later unless it has been recently repotted and you absolutely know the roots are healthy.