PHP offers both simple helpers like file_get_contents() and file_put_contents(), and lower-level stream functions fopen()/fread()/fwrite()/fclose() for finer control over large files. File existence and permissions can be checked with file_exists() and is_writable().
When working with user-uploaded paths or file names, always validate and sanitize them to prevent path traversal attacks (e.g., '../../etc/passwd').