The was no "close reader" command but its possible to use a wrapper function to kill task, however its better to invoke clean close F4 via send keys, as per other answers.Here is latest source of Command Line Switches
This article describes the protected PDF readers that are supported for Azure Information Protection (AIP). Protected PDF readers enable users to open those encrypted PDFs and view the sensitive information contained.
Encrypting your PDFs with AIP ensures that unauthorized people cannot read the file's content. Protected PDF readers that support AIP verify that you've been granted permissions to open the document, and also decrypt the content for you.
If you're unable to open your protected PDF using the recommended reader, the document may be protected in a previous format. For example, Microsoft SharePoint currently uses an older format for PDF documents in IRM-protected libraries.
Adobe Acrobat Reader Lite is a free software used for viewing, printing and annotating PDF files. Developed by Adobe, Adobe Reader Lite is a stripped version of the popular Adobe Reader DC (Document Cloud), bringing you all the essential tools to interact with PDFs but without the unnecessary bloat and resource-demanding features that the latter is known for. Considered the leading PDF reader in the market, Adobe Reader Lite is the go-to choice for everyone looking for a powerful document management application that will go light on their computer resources. Would you like to know more?