Currency depreciation do not affect the PPP GDP. Pakistan's nominal GDP declined but not the PPP GDP. Bangladesh's nominal GDP crossed Pakistan earlier than expected because of massive depreciation of Pak Rupee against Dollar. But PPP is unaffected by this development. But Bangladesh's per PPP will also cross Pakistan within few years if current gap of GDP growth persists.
Even if Pakistan had not undergone massive depreciation of rupee, still Bangladesh's nominal GDP per Capita would have been somewhat higher than Pakistan. Because Bangladesh's economy somewhat more integrated with world market. So there is comparatively less gap in actual value and exchange rate value of Bangladesh's national currency Taka compared to Pakistan or India. That's why Taka's PPP factor is less compared to Indian or Pakistani rupee. In other word, 1000 dollar has somewhat less purchasing power in Bangladesh compared to India or Pakistan. This less purchasing power of 1 dollar in Bangladesh means, goods in Bangladesh are comparatively pricier than Bangladesh. But not all goods, some goods which Bangladesh import or artificially priced up by a lot of govt. tax. When IMF or World Bank calculate PPP factor, they take into consideration of price of a range of products and services.
The ratio between per capita ppp and per capita nominal in 3 countries-
Bangladesh-2.64
India-3.85
Pakistan-4.30
This means, Pakistani Rupee is most undervalued against dollar among three currencies, then Indian Rupee and Bangladeshi taka is comparatively less undervalued against dollar.
@Bengal71