Absolutely, it is by all means a DIY job
You can find door seals on places like eBay for cheap. They can be a little bit fiddly to replace however with some patience it's definitely doable at home. However before you shell out on one, is yours visibly damaged? If not, sometimes the door itself may not be sitting right. Check that the door is not sitting proud from the car particularly the area that is leaking and that the gaps are all even as this can lead to leaks. This video explains that in detail.
If the door is all fine and there is still a leak then you'd be better off fitting a replacement seal. Used ones generally do the trick. Would be pretty expensive and/or difficult to get a new seal. There are a ton of guides out there on YouTube and even this forum on replacing door seals.
Alternatively, you can fill the old seals. I've had success doing this in the past. Just ensure the foam (Caulk Saver) you use isn't too big otherwise that would cause issues. Watch this;
All the best!