Are you converting or complex 3D geometry ?
DWG to PLN converters vary; the best are accurate, preserve layers/blocks, and handle scale/units well. Expect tradeoffs between price, ease of use, and fidelity.
There are several online converters available. However, their effectiveness is limited. While tools like CloudConvert support a variety of CAD formats, and AnyConv offers free online tools, they generally struggle with the complexity of BIM data. They might convert the drawing geometry, but will likely lose "intelligence" (walls won't be recognized as walls, properties might vanish). As a general rule, using a dedicated desktop application like ArchiCAD is strongly recommended for professional results.
The most reliable way to convert a DWG file into a PLN file is by using Graphisoft Archicad itself. This ensures that layers, scales, and line types translate accurately. Step 1: Prepare the DWG File in AutoCAD
Explode complex blocks in AutoCAD before converting, or import them as Archicad Objects. Hidden layers, hatches, and redundant lines.