There are three ways to source with Paradigm, Particles, VDBs, Houdini Height Fields, and primitive shapes that come with the Paradigm toolset called Source Shapes.
You can connect particles to the 3rd input of the solver. You can create these any way you want however there are a few things to keep in mind.
If you give the solver points to source it will emit all the particles every time step.
If you wish to emit particles only on the first frame you will need to animate the source to achieve this.
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Remember that with the pressure force if you continuously emit particles in the same location overlapping particles will cause an expansive force in order to maintain the particles separation. If you need to continuously emit it’s recommended to make the particles separation of the source point cloud larger than the simulation particle division size.
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Currently the only thing other than the particle position you can source is particle velocity. You should name the float vector 3 attribute “v” in line with Houdini conventions.
You can connect VDBs directly into the first input of the solver. You can make these sources any way you want. It can be sourced using OpenVDB or on the GPU using NanoVDB which is on by default.
The solver will only accept these names for default sourcing. It is case-sensitive.