Improve the default name of downloaded PDF files?

Can we get the default names for invoices and estimates downloaded to actually include the word "estimate" or "invoice" just to make it easier to distinguish between them in my downloads folder?

Currently the invoices and estimates follow the format:

${name-of-company}_${id}.pdf

If we could get:

${name-of-company}_estimate_${id}.pdf

and

${name-of-company}_invoice_${id}.pdf

..the problem would be solved!