Adobe Acrobat reader DC

While opening a .pdf file, I'm getting error message as:

"There was an error opening this document. The security plug-in required by this command is unavailable."

Please help to install the required plug-in, if any. Need urgent support to resolve the issues as I cannot open multiple files even after uninstalling and rebooting my laptop. 

The other files I have were able to open but not few files. 

Please respond at earliest. OR, help to convert .acsm files to .pdf files. The initial files were downloaded as .acsm files and was then opened on adobe digital.