How can I convert a rasterized smoke volume to a polygon soup? I checked the properties of rasterize node and it shows two VDBs. However, when I use the convert VDB node, it doesn't convert it into polygons. I tried convert volume node also but still it doesn't convert it into polygons.

Hello.
Just give the Isovalue option in VDB Convert a small positive number like 0.001.

is it your intention to convert source volume to polygon or the simulated smoke?
because currently you are doing it on source, which is VDB so Convert VDB as you have it should work, but you need to increase isovalue since you are dealing with fog volume whose values are >=0 so no iso surface can be created exactly at 0

if however you want to convert the resulting smoke you need to work in pyro_input object
volumes from sim are houdini volumes though so you can use Convert SOP, Convert Volume SOP or convert to VDB volume first and then Convert VDB to polygons
all of them with isovalue > 0

attached a file with both

Thanks. Yes. I wanted to convert the resultant smoke only. Your workflow is quite interesting and gives the desired final geometry. I'll have to spend more time in order to understand more nodes of pyros and its related workflows to build such systems of nodes.

How can the resolution of the converted volume be increased so that the resultant polygon conversion is smoother, cleaner and denser?

Currently it looks like this.