Search for "Bosch KL 1206 original manual" on eBay. Prices range from $10 to $30. Vintage tool sellers sometimes include a photocopy when you buy a refurbished unit—ask them for a scan.
If you need a copy of the specific document for your records or secondary functions (like hammering/drilling if using the power tool variant), you can search official databases: Power Tool Variant : For the KL 1206 drill/driver, search by the part number (found on the nameplate) on the Bosch Professional Manual Search Home/Auto Variant E-NR (model number) Bosch Home Support portal to download technical documentation. Bosch Home