Read document from base 64 decoded string : R

Question

Can anyone please help me in resolving the issue for opening and reading the document from decoded string in R?

Example :

1. Upload a document from HTML page and get encoded string of document as data URL in JS.
2. Encoded string is passed to R code through REST API.
3. Got a decoded URL string for a uploaded document in R code using base64decode.

Now, the problem is how to read any document from base64 decoded URL string in R? OR How to deal with encoded URL string to read original data of any document in R?