Clean up repository structure and release docs

sources/core/PDFFileSelection.swift

@@ -0,0 +1,19 @@
+import Foundation
+import UniformTypeIdentifiers
+
+public enum PDFFileSelection {
+    public static func isPDFFileURL(_ url: URL) -> Bool {
+        guard url.isFileURL else { return false }
+
+        let resourceValues = try? url.resourceValues(forKeys: [.contentTypeKey, .isDirectoryKey])
+        if resourceValues?.isDirectory == true {
+            return false
+        }
+
+        if let contentType = resourceValues?.contentType {
+            return contentType.conforms(to: .pdf)
+        }
+
+        return url.pathExtension.localizedCaseInsensitiveCompare("pdf") == .orderedSame
+    }
+}