diff --git a/src/Everything2Everything.Core/Converters/ExternalProcessRunner.cs b/src/Everything2Everything.Core/Converters/ExternalProcessRunner.cs
new file mode 100644
index 0000000..361dd22
--- /dev/null
+++ b/src/Everything2Everything.Core/Converters/ExternalProcessRunner.cs
@@ -0,0 +1,79 @@
+using System.Diagnostics;
+using System.Text;
+
+namespace Everything2Everything.Core.Converters;
+
+public sealed record ProcessRunResult(int ExitCode, string StdOut, string StdErr, bool TimedOut)
+{
+    public bool Success => !TimedOut && ExitCode == 0;
+}
+
+/// <summary>
+/// 외부 CLI 프로세스 실행을 일원화한다 — stdout/stderr 수집, 타임아웃, 취소 시 프로세스 트리 종료.
+/// LibreOffice·FFmpeg·Ghostscript·qpdf 등 모든 외부 도구 어댑터가 공유하는 실행기.
+/// </summary>
+public static class ExternalProcessRunner
+{
+    public static async Task<ProcessRunResult> RunAsync(
+        string fileName,
+        IEnumerable<string> arguments,
+        TimeSpan? timeout = null,
+        string? workingDirectory = null,
+        CancellationToken cancellationToken = default)
+    {
+        var psi = new ProcessStartInfo
+        {
+            FileName = fileName,
+            UseShellExecute = false,
+            CreateNoWindow = true,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+        };
+        foreach (var a in arguments) psi.ArgumentList.Add(a);
+        if (!string.IsNullOrEmpty(workingDirectory)) psi.WorkingDirectory = workingDirectory;
+
+        using var proc = new Process { StartInfo = psi };
+        var stdout = new StringBuilder();
+        var stderr = new StringBuilder();
+        proc.OutputDataReceived += (_, e) => { if (e.Data is not null) stdout.AppendLine(e.Data); };
+        proc.ErrorDataReceived += (_, e) => { if (e.Data is not null) stderr.AppendLine(e.Data); };
+
+        if (!proc.Start())
+            throw new InvalidOperationException($"프로세스를 시작하지 못했습니다: {fileName}");
+
+        proc.BeginOutputReadLine();
+        proc.BeginErrorReadLine();
+
+        using var linked = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+        if (timeout is { } t) linked.CancelAfter(t);
+
+        var timedOut = false;
+        try
+        {
+            await proc.WaitForExitAsync(linked.Token).ConfigureAwait(false);
+        }
+        catch (OperationCanceledException)
+        {
+            // 사용자 취소면 전파, 타임아웃이면 TimedOut으로 보고
+            timedOut = !cancellationToken.IsCancellationRequested;
+            try { proc.Kill(entireProcessTree: true); } catch { /* 이미 종료 */ }
+            if (cancellationToken.IsCancellationRequested)
+            {
+                try { proc.WaitForExit(2000); } catch { }
+                throw;
+            }
+        }
+
+        // Kill 또는 종료 후 비동기 출력 콜백이 마저 도착하도록 잠깐 대기
+        try { proc.WaitForExit(2000); } catch { }
+
+        var exitCode = timedOut ? -1 : SafeExitCode(proc);
+        return new ProcessRunResult(exitCode, stdout.ToString(), stderr.ToString(), timedOut);
+    }
+
+    private static int SafeExitCode(Process proc)
+    {
+        try { return proc.ExitCode; }
+        catch { return -1; }
+    }
+}
diff --git a/src/Everything2Everything.Core/Everything2Everything.Core.csproj b/src/Everything2Everything.Core/Everything2Everything.Core.csproj
index dc1e9ad..12a9a38 100644
--- a/src/Everything2Everything.Core/Everything2Everything.Core.csproj
+++ b/src/Everything2Everything.Core/Everything2Everything.Core.csproj
@@ -24,6 +24,7 @@
     <PackageReference Include="ReverseMarkdown" Version="4.6.0" />
     <PackageReference Include="PDFsharp" Version="6.2.0" />
     <PackageReference Include="Svg.Skia" Version="5.0.0" />
+    <PackageReference Include="System.Security.Cryptography.ProtectedData" Version="10.0.8" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/Everything2Everything.Core/SettingsStore.cs b/src/Everything2Everything.Core/SettingsStore.cs
new file mode 100644
index 0000000..e7fb48b
--- /dev/null
+++ b/src/Everything2Everything.Core/SettingsStore.cs
@@ -0,0 +1,92 @@
+using System.Security.Cryptography;
+using System.Text.Json;
+
+namespace Everything2Everything.Core;
+
+/// <summary>키-값 설정 저장소. API 키·외부 도구 경로 등 민감 정보를 영속화한다.</summary>
+public interface ISettingsStore
+{
+    string? Get(string key);
+    void Set(string key, string value);
+    void Remove(string key);
+    bool Contains(string key);
+}
+
+/// <summary>
+/// DPAPI(CurrentUser)로 암호화해 %LOCALAPPDATA%\Everything2Everything\settings.dat 에 저장한다.
+/// 현재 사용자 계정에서만 복호화 가능하므로 API 키 저장에 적합하다. Windows 전용.
+/// </summary>
+public sealed class DpapiSettingsStore : ISettingsStore
+{
+    private readonly string _path;
+    private readonly Dictionary<string, string> _cache;
+    private readonly object _lock = new();
+
+    public DpapiSettingsStore(string? filePath = null)
+    {
+        _path = filePath ?? DefaultPath();
+        _cache = Load(_path);
+    }
+
+    public static string DefaultPath()
+    {
+        var dir = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+            "Everything2Everything");
+        Directory.CreateDirectory(dir);
+        return Path.Combine(dir, "settings.dat");
+    }
+
+    public string? Get(string key)
+    {
+        lock (_lock) return _cache.TryGetValue(key, out var v) ? v : null;
+    }
+
+    public bool Contains(string key)
+    {
+        lock (_lock) return _cache.ContainsKey(key);
+    }
+
+    public void Set(string key, string value)
+    {
+        lock (_lock)
+        {
+            _cache[key] = value;
+            Save();
+        }
+    }
+
+    public void Remove(string key)
+    {
+        lock (_lock)
+        {
+            if (_cache.Remove(key)) Save();
+        }
+    }
+
+    private void Save()
+    {
+        var json = JsonSerializer.SerializeToUtf8Bytes(_cache);
+        var encrypted = ProtectedData.Protect(json, optionalEntropy: null, DataProtectionScope.CurrentUser);
+        var tmp = _path + ".tmp";
+        File.WriteAllBytes(tmp, encrypted);
+        if (File.Exists(_path)) File.Delete(_path);
+        File.Move(tmp, _path);
+    }
+
+    private static Dictionary<string, string> Load(string path)
+    {
+        try
+        {
+            if (!File.Exists(path)) return new(StringComparer.Ordinal);
+            var encrypted = File.ReadAllBytes(path);
+            var json = ProtectedData.Unprotect(encrypted, optionalEntropy: null, DataProtectionScope.CurrentUser);
+            return JsonSerializer.Deserialize<Dictionary<string, string>>(json) ?? new(StringComparer.Ordinal);
+        }
+        catch
+        {
+            // 손상/복호화 실패 시 빈 저장소로 시작(설정은 비치명적)
+            return new(StringComparer.Ordinal);
+        }
+    }
+}
diff --git a/src/Everything2Everything.Tests/InfraTests.cs b/src/Everything2Everything.Tests/InfraTests.cs
new file mode 100644
index 0000000..442119e
--- /dev/null
+++ b/src/Everything2Everything.Tests/InfraTests.cs
@@ -0,0 +1,96 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Everything2Everything.Core;
+using Everything2Everything.Core.Converters;
+using Xunit;
+
+namespace Everything2Everything.Tests;
+
+public class SettingsStoreTests
+{
+    private static string TempFile()
+        => Path.Combine(Path.GetTempPath(), "e2e_settings_" + Guid.NewGuid().ToString("N") + ".dat");
+
+    [Fact]
+    public void Set_Get_Roundtrip_AndPersists()
+    {
+        var path = TempFile();
+        try
+        {
+            var store = new DpapiSettingsStore(path);
+            store.Set("openai.key", "sk-secret-123");
+            Assert.Equal("sk-secret-123", store.Get("openai.key"));
+            Assert.True(store.Contains("openai.key"));
+
+            // 새 인스턴스로 다시 로드 — 영속 + 복호화 확인
+            var reloaded = new DpapiSettingsStore(path);
+            Assert.Equal("sk-secret-123", reloaded.Get("openai.key"));
+        }
+        finally { try { File.Delete(path); } catch { } }
+    }
+
+    [Fact]
+    public void File_IsEncrypted_NotPlaintext()
+    {
+        var path = TempFile();
+        try
+        {
+            new DpapiSettingsStore(path).Set("k", "PLAINTEXT_MARKER");
+            var bytes = File.ReadAllBytes(path);
+            var asText = System.Text.Encoding.UTF8.GetString(bytes);
+            Assert.DoesNotContain("PLAINTEXT_MARKER", asText);
+        }
+        finally { try { File.Delete(path); } catch { } }
+    }
+
+    [Fact]
+    public void Remove_DeletesKey()
+    {
+        var path = TempFile();
+        try
+        {
+            var store = new DpapiSettingsStore(path);
+            store.Set("k", "v");
+            store.Remove("k");
+            Assert.Null(store.Get("k"));
+            Assert.False(store.Contains("k"));
+        }
+        finally { try { File.Delete(path); } catch { } }
+    }
+}
+
+public class ExternalProcessRunnerTests
+{
+    [Fact]
+    public async Task Echo_CapturesStdout_AndExitZero()
+    {
+        var r = await ExternalProcessRunner.RunAsync(
+            "cmd.exe", new[] { "/c", "echo", "hello_e2e" },
+            timeout: TimeSpan.FromSeconds(10), cancellationToken: CancellationToken.None);
+        Assert.True(r.Success);
+        Assert.Equal(0, r.ExitCode);
+        Assert.Contains("hello_e2e", r.StdOut);
+    }
+
+    [Fact]
+    public async Task NonZeroExit_IsReported()
+    {
+        var r = await ExternalProcessRunner.RunAsync(
+            "cmd.exe", new[] { "/c", "exit", "3" },
+            timeout: TimeSpan.FromSeconds(10), cancellationToken: CancellationToken.None);
+        Assert.False(r.Success);
+        Assert.Equal(3, r.ExitCode);
+    }
+
+    [Fact]
+    public async Task Timeout_IsDetected_AndProcessKilled()
+    {
+        var r = await ExternalProcessRunner.RunAsync(
+            "cmd.exe", new[] { "/c", "ping", "127.0.0.1", "-n", "10" },
+            timeout: TimeSpan.FromMilliseconds(400), cancellationToken: CancellationToken.None);
+        Assert.True(r.TimedOut);
+        Assert.False(r.Success);
+    }
+}