diff --git a/modules/home/users/crumb/default-applications.nix b/modules/home/users/crumb/default-applications.nix
new file mode 100644
index 0000000..d4db28a
--- /dev/null
+++ b/modules/home/users/crumb/default-applications.nix
@@ -0,0 +1,20 @@
+{ config, lib, pkgs, ... }:
+
+let cfg = config.sydnix.users.crumb.default-applications;
+in {
+  options.sydnix.users.crumb.default-applications = {
+    enable = lib.mkEnableOption "Default mime-type applications";
+  };
+
+  config = lib.mkIf cfg.enable {
+    xdg.mimeApps = {
+      enable = true;
+      defaultApplications = {
+        "application/pdf" = [
+          "emacsclient.desktop"
+          "emacs.desktop"
+        ];
+      };
+    };
+  };
+}
diff --git a/modules/home/users/crumb/emacs.nix b/modules/home/users/crumb/emacs.nix
index c46bcf4..4fa464b 100755
--- a/modules/home/users/crumb/emacs.nix
+++ b/modules/home/users/crumb/emacs.nix
@@ -152,5 +152,13 @@ in {
         ec = "emacsclient";
         em = "emacs";
       };
+
+      # Mark Emacs as a valid PDF reader.
+      xdg.mimeApps.associations.added = {
+        "application/pdf" = [
+          "emacsclient.desktop"
+          "emacs.desktop"
+        ];
+      };
     });
 }
diff --git a/users/crumb/default.nix b/users/crumb/default.nix
index 04c99ef..4aea087 100755
--- a/users/crumb/default.nix
+++ b/users/crumb/default.nix
@@ -47,6 +47,7 @@
       # Personal configurations.
       users.crumb = {
         age.enable = true;
+        default-applications.enable = true;
         fcitx5.enable = true;
         bash.enable = true;
         direnv.enable = true;