A GDR works mechanically like an adr but targets international rather than specifically US investors. Many are placed under exemptions that restrict them to qualified institutional buyers, so retail access and liquidity can be thin even when the underlying local stock is heavily traded.
GDRs are common for issuers from markets with capital controls or restricted foreign ownership, where the receipt is the only practical way for an outside investor to hold the exposure.
Example: a GDR represents 5 local shares trading at 220 local units, with 82 local units to the dollar. Fair value is 5 x 220 / 82 = $13.41, and the GDR quote should track that figure as the currency moves.
Related: adr, adr-ratio, foreign-ordinary-shares, cross-listing, dual-listing