Error while reading a file using system.file function

I am referring to an R code available on https://rdrr.io/bioc/ATACseqQC/man/TSSEscore.html where reading the file is suggested as:

bamfile <- system.file("extdata", "GL1.bam", 
                       package="ATACseqQC", mustWork=TRUE)

When I am trying to do this on my file as below it gives me an error

bamfile <- system.file("extdata", "RRrep1_rmDupChrC_sorted.bam", package="ATACseqQC", mustWork=TRUE)

Error in system.file("extdata", "RRrep1_rmDupChrC_sorted.bam", package = "ATACseqQC",  : 
  no file found

list.files()
[1] "RRrep1_rmDupChrC_sorted.bam"

Please help me to understand why system.file function does not allow to read my file.