Using class to download documents !

Hi,

I have a fairly simple requirement.

I need to download specifc documents based on LOIO or PHIO id from SOLAR01 into an internal table.

I found some FM which I believe will work.

CL_CRM_DOCUMENTS ->GET_WITH_TABLE

In the Get method, it is asking object id and document class.

I have the object id with me, but where will i retrieve the document class.

Let me know if there is any other way apart from this.

The method is using structure SKWF_IO for input parameters.

Regards

Krish