Some e-books sold on internet can be delivered as .acsm files, which means that they work only with the Adobe Digital Platform. These files actually cannot be converted to any other electronic book format (such as pdf format in this case), because .acsm files do not represents the actual e-books. They are just authorized links so the user can download and legally view purchased books on their computers.
As far as we know, there is no other way to convert acsm to pdf without Adobe Digital Editions. The only way to sort of convert acsm to pdf would be to install Adobe Digital Editions and authorize your computer with your Adobe ID, then open the .acsm file and load it in the program.
After the book is downloaded to your computer, you can find it either in PDF or ePUB form in the default Adobe Edition location in user account and documents, which more or less achieves the acsm to pdf conversion you are looking for.
Sometimes you will also have to remove DRM protection from pdf document, because these files are still protected by Adobe DRM which causes troubles when reading the file on Mac or Kindle platform.
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