You download a ebook from public Library, what you are really downloading is an .acsm file. .acsm is not your actual eBook. It is just a link to your eBook that allows a program like Digital Editions to download the actual book, When Digital Editions sees the .acsm file it will automatically download the PDF or ePUB file, which is the actual eBook, so you only remove drm from epub/pdf file, not from .acsm file, This is how to remove drm from epub/pdf file.
PDF ePub DRM Removal is tools to remove DRM protection and remove expired limitation of public library epub/PDF books. you can download it at here.
1). Install Adobe Digital editions, you can skip to next step if you have already installed.
2). Open .acsm file in digital editions, When Digital Editions sees the .acsm file it will automatically download the PDF or ePUB file, which is the actual eBook, and then unlock the file’s DRM so that it becomes readable. At this point you should be able to read the library book in Digital Editions.
3). Run PDF ePub DRM Removal, it is easy to use, just select public library epub file from digital editions library folder, and click “Remove DRM” button.
4) When you’re ready to removal DRM protection , click “Removal DRM” button. After a few seconds, you’ll have an ePub/PDF book in output folder.
5) Once find decrypted ePub/PDF file in Windows Explorer, you can upload it to e-reader device or convert to other format, enjoy reading.