Lotus Domino API - Parsing through NotesItems
You can rewrite the nested ifs and loops with a nice and short LINQ query that will give you all the items first:

var items
    from doc in notedb.AllDocuments.Where(doc =&gt; doc.Items != null)
    from item in doc.Items.Where(item =&gt; item.Values != null)
    select item;


Then, you loop over the items with a foreach loop:

foreach (var item in items)
{
    SetDocProperty(pdbdoc, item);
}


and call a new helper method that encapsulates the switch:

void SetDocProperty(SomeType pdbdoc, SomeOtherType item)
{
    switch (item.Name)
    {
        //PDB DATA
        case "DocArea": pdbdoc.DocArea = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocDisc": pdbdoc.DocDisc = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocObject": pdbdoc.DocObject = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocOrigin": pdbdoc.DocOrigin = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocRef": pdbdoc.DocRef = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocRefClient": pdbdoc.DocRefClient = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocRevDt": pdbdoc.DocRevDt = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocRevNo": pdbdoc.DocRevNo = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocTitle": pdbdoc.DocTitle = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocUnit": pdbdoc.DocUnit = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "INCABINET": pdbdoc.InCabinet = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        //VDB DATA
        case "VendorDocNm": pdbdoc.DocTitle = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "VendorDocRef": pdbdoc.DocRefClient = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "VendorDocRevNo": pdbdoc.DocRevNo = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "DocUse": pdbdoc.DocObject = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "VendorDocRevDt": pdbdoc.DocRevDt = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "VendorDocClientRef": pdbdoc.DocRef = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
        case "VendorNm": pdbdoc.VendorName = LotusUtils.LotusUtils.LotusItemToString(item.Values); break;
    }
}


You could probably parallelize it with Parallel.ForEach but the code isn't complete so I cannot make any other suggestions as I don't know how the pdbdoc works and what it is.