Parcels sent to Bulgaria, you need the original invoice, the invoice must be printed (not handwritten), indicate the terms of trade (such as FOB, etc.). Attached invoice requirements: delivery company logo (head units), date, invoice number, the recipient and the sender details (company name / address, etc.), producer, trademark brand, the product detailed description name, product number quantity, FOB value, weight, type, sealed and signed. Comm Inv must include Shprs Logo, C / I Number, date of issue, full shpr & cnees info (name, address), MFG country & brand, full description of prods per item and or harmonized codes, contents, qty, FOB value, weight, and model. 
Bulgaria needs to provide the original commercial invoice, the invoice to indicate the freight