Attach document on list page in ax 2012 R3

Step 1. Go To table that you are using as list page datasource and create display method.

//BP Deviation Documented
display smmDocIconNum showDocHandIcon()
{
#macrolib.resource
;
if ((select firstonly docuRef where docuRef.RefCompanyId == this.DataAreaId && docuRef.RefTableId == this.TableId && docuRef.RefRecId == this.RecId).RecId)
{
return #RES_NODE_DOC;
}

return #RES_AM_NEW;
}

Step 2: Now go to list page form > Designs >Design  > Grid > New Control > Window >

Step 3: Set window control properties Like

width : 15

height : 15

VerticalSpacing : 0

Label : Documents

DataSource : Which is used by Form

DataMethod : showDocHandIcon

Step 4 : Go to WindowControl > Method > Override Method > MouseUp >

write the code

int mouseUp(int _x, int _y, int _button, boolean _ctrl, boolean _shift)
{
CustTable custTable; // use your table

int ret;

ret = super(_x, _y, _button, _ctrl, _shift);

PurchRFQCaseTableForm::openDocHandling(custTable, element);

return ret;
}