Adobe PageMaker has been officially discontinued years ago and PageMaker documents (.pmd) are not well supported in other software, which makes conversion of .pmd files tedious thing to do, especially if you do not have access to the original program.
You can certainly convert (export) pmd to txt in PageMaker with the default Save as.. / Export function. Unfortunately, we have no information about any 3rd party software that would be capable of the same.Open PMD file Open TXT file
One of the first desktop publishing programs on market
Mac version of once popular publishing program