diff --git a/src/Backend/SolutionErp.Api/Controllers/PurchaseEvaluationsController.cs b/src/Backend/SolutionErp.Api/Controllers/PurchaseEvaluationsController.cs
index 511d991..dbe1260 100644
--- a/src/Backend/SolutionErp.Api/Controllers/PurchaseEvaluationsController.cs
+++ b/src/Backend/SolutionErp.Api/Controllers/PurchaseEvaluationsController.cs
@@ -52,6 +52,18 @@ public class PurchaseEvaluationsController(IMediator mediator) : ControllerBase
         return NoContent();
     }
 
+    // S22+4 — Feature 2: Section "Điều chỉnh ngân sách" tách endpoint riêng.
+    // Cho phép Drafter (DangSoanThao/TraLai) OR Approver currentLevel (ChoDuyet)
+    // OR Admin adjust Budget* fields. Handler kiểm phase + actor scope.
+    [HttpPatch("{id:guid}/budget-adjust")]
+    public async Task<IActionResult> AdjustBudget(Guid id, [FromBody] AdjustBudgetBody body, CancellationToken ct)
+    {
+        await mediator.Send(new AdjustPurchaseEvaluationBudgetCommand(
+            id, body.BudgetId, body.BudgetManualName, body.BudgetManualAmount), ct);
+        return NoContent();
+    }
+    public record AdjustBudgetBody(Guid? BudgetId, string? BudgetManualName, decimal? BudgetManualAmount);
+
     [HttpPost("{id:guid}/transitions")]
     public async Task<IActionResult> Transition(Guid id, [FromBody] TransitionPeBody body, CancellationToken ct)
     {
@@ -182,6 +194,17 @@ public class PurchaseEvaluationsController(IMediator mediator) : ControllerBase
         return File(f.Content, f.ContentType, f.FileName);
     }
 
+    // S22+4 — Inline view endpoint cho FE preview modal (PDF iframe, image <img>).
+    // Cùng handler download, khác Content-Disposition (inline vs attachment).
+    // Permission: same actor scope như GET phiếu (Plan E V2 strict).
+    [HttpGet("{id:guid}/attachments/{attId:guid}/view")]
+    public async Task<IActionResult> ViewAttachment(Guid id, Guid attId, CancellationToken ct)
+    {
+        var f = await mediator.Send(new DownloadPurchaseEvaluationAttachmentQuery(id, attId), ct);
+        Response.Headers["Content-Disposition"] = $"inline; filename=\"{f.FileName}\"";
+        return File(f.Content, f.ContentType);
+    }
+
     [HttpDelete("{id:guid}/attachments/{attId:guid}")]
     public async Task<IActionResult> DeleteAttachment(Guid id, Guid attId, CancellationToken ct)
     {
diff --git a/src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationFeatures.cs b/src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationFeatures.cs
index eb590c6..6b7fc55 100644
--- a/src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationFeatures.cs
+++ b/src/Backend/SolutionErp.Application/PurchaseEvaluations/PurchaseEvaluationFeatures.cs
@@ -239,6 +239,146 @@ public class UpdatePurchaseEvaluationDraftCommandHandler(
     }
 }
 
+// ========== ADJUST BUDGET (S22+4 — Feature 2) ==========
+// Section "Điều chỉnh ngân sách" cho phép sửa BudgetId + BudgetManualName +
+// BudgetManualAmount khi:
+//   - Drafter scope (Phase=DangSoanThao OR TraLai) — actor là Drafter của phiếu
+//   - Approver scope (Phase=ChoDuyet) — actor là ApproverUserId của currentLevel
+//   - Admin → bypass
+//
+// Tách endpoint riêng (KHÔNG dùng UpdatePeDraft) vì UpdatePeDraft chỉ accept
+// DangSoanThao/TraLai phase + cập nhật cả Section 1 (TenGoiThau, DiaDiem,
+// MoTa, PaymentTerms) — Approver KHÔNG nên được edit các field đó khi đang duyệt.
+// AdjustBudget chỉ adjust Budget* — narrow scope hợp lý.
+public record AdjustPurchaseEvaluationBudgetCommand(
+    Guid Id,
+    Guid? BudgetId,
+    string? BudgetManualName,
+    decimal? BudgetManualAmount) : IRequest;
+
+public class AdjustPurchaseEvaluationBudgetCommandValidator : AbstractValidator<AdjustPurchaseEvaluationBudgetCommand>
+{
+    public AdjustPurchaseEvaluationBudgetCommandValidator()
+    {
+        RuleFor(x => x.BudgetManualName).MaximumLength(200);
+        RuleFor(x => x.BudgetManualAmount).GreaterThanOrEqualTo(0).When(x => x.BudgetManualAmount.HasValue);
+    }
+}
+
+public class AdjustPurchaseEvaluationBudgetCommandHandler(
+    IApplicationDbContext db,
+    ICurrentUser currentUser) : IRequestHandler<AdjustPurchaseEvaluationBudgetCommand>
+{
+    public async Task Handle(AdjustPurchaseEvaluationBudgetCommand request, CancellationToken ct)
+    {
+        var entity = await db.PurchaseEvaluations.FirstOrDefaultAsync(x => x.Id == request.Id, ct)
+            ?? throw new NotFoundException("PurchaseEvaluation", request.Id);
+
+        var isAdmin = currentUser.Roles.Contains(AppRoles.Admin);
+        var isDrafter = currentUser.UserId is Guid uid && entity.DrafterUserId == uid;
+        var actorTag = string.Empty;
+
+        if (!isAdmin)
+        {
+            if (entity.Phase == PurchaseEvaluationPhase.DangSoanThao
+                || entity.Phase == PurchaseEvaluationPhase.TraLai)
+            {
+                // Drafter scope — chỉ Drafter của phiếu được adjust
+                if (!isDrafter)
+                    throw new ForbiddenException("Chỉ Drafter của phiếu được điều chỉnh ngân sách khi Nháp/Trả lại.");
+                actorTag = "[Drafter]";
+            }
+            else if (entity.Phase == PurchaseEvaluationPhase.ChoDuyet)
+            {
+                // Approver scope — actor phải là ApproverUserId của currentLevel
+                if (entity.ApprovalWorkflowId is not Guid awId)
+                    throw new ConflictException("Phiếu V1 legacy không hỗ trợ điều chỉnh ngân sách lúc đang duyệt.");
+                if (entity.CurrentWorkflowStepIndex is not int csi || entity.CurrentApprovalLevelOrder is not int curLvl)
+                    throw new ConflictException("Phiếu chưa init pointer workflow.");
+                if (currentUser.UserId is not Guid actorId)
+                    throw new ConflictException("Yêu cầu authenticated user.");
+
+                var workflow = await db.ApprovalWorkflows.AsNoTracking()
+                    .Include(w => w.Steps).ThenInclude(s => s.Levels)
+                    .FirstOrDefaultAsync(w => w.Id == awId, ct)
+                    ?? throw new NotFoundException("ApprovalWorkflow", awId);
+                var stepsOrdered = workflow.Steps.OrderBy(s => s.Order).ToList();
+                if (csi < 0 || csi >= stepsOrdered.Count)
+                    throw new ConflictException("Pointer step out of range — schema lỗi.");
+                var step = stepsOrdered[csi];
+                var level = step.Levels.FirstOrDefault(l => l.Order == curLvl);
+                if (level?.ApproverUserId != actorId)
+                    throw new ForbiddenException(
+                        $"Chỉ NV phụ trách Bước {step.Order} / Cấp {curLvl} mới được điều chỉnh ngân sách lúc đang duyệt.");
+                actorTag = $"[Approver Bước {step.Order}/Cấp {curLvl}]";
+            }
+            else
+            {
+                throw new ConflictException(
+                    $"Phase={entity.Phase} không cho phép điều chỉnh ngân sách. " +
+                    "Chỉ cho phép khi Nháp/Trả lại (Drafter) hoặc Đang duyệt (Approver).");
+            }
+        }
+        else
+        {
+            actorTag = "[Admin]";
+        }
+
+        // Validate Budget link nếu thay đổi
+        if (request.BudgetId is Guid bid && bid != entity.BudgetId)
+        {
+            var bg = await db.Budgets.AsNoTracking()
+                .FirstOrDefaultAsync(b => b.Id == bid, ct)
+                ?? throw new NotFoundException("Budget", bid);
+            if (bg.ProjectId != entity.ProjectId)
+                throw new ConflictException("Ngân sách phải cùng dự án với phiếu.");
+            if (bg.Phase != Domain.Budgets.BudgetPhase.DaDuyet)
+                throw new ConflictException("Chỉ link được ngân sách đã duyệt.");
+        }
+
+        // Capture old + apply
+        var oldBudgetId = entity.BudgetId;
+        var oldBudgetManualName = entity.BudgetManualName;
+        var oldBudgetManualAmount = entity.BudgetManualAmount;
+
+        entity.BudgetId = request.BudgetId;
+        entity.BudgetManualName = request.BudgetManualName;
+        entity.BudgetManualAmount = request.BudgetManualAmount;
+
+        // Audit changelog with diff (Vietnamese friendly format)
+        var parts = new List<string>();
+        if (oldBudgetId != request.BudgetId)
+        {
+            var oldDesc = oldBudgetId is null ? "(chưa link)" : "Budget#" + oldBudgetId.Value.ToString()[..8];
+            var newDesc = request.BudgetId is null ? "(huỷ link)" : "Budget#" + request.BudgetId.Value.ToString()[..8];
+            parts.Add($"link {oldDesc} → {newDesc}");
+        }
+        if (oldBudgetManualName != request.BudgetManualName)
+        {
+            parts.Add($"tên \"{oldBudgetManualName ?? "(trống)"}\" → \"{request.BudgetManualName ?? "(trống)"}\"");
+        }
+        if (oldBudgetManualAmount != request.BudgetManualAmount)
+        {
+            var oldAmt = oldBudgetManualAmount?.ToString("N0") ?? "(trống)";
+            var newAmt = request.BudgetManualAmount?.ToString("N0") ?? "(trống)";
+            parts.Add($"số tiền {oldAmt}đ → {newAmt}đ");
+        }
+        var diffSummary = parts.Count == 0 ? "không đổi" : string.Join(", ", parts);
+
+        db.PurchaseEvaluationChangelogs.Add(new PurchaseEvaluationChangelog
+        {
+            PurchaseEvaluationId = entity.Id,
+            EntityType = PurchaseEvaluationEntityType.Header,
+            Action = ChangelogAction.Update,
+            PhaseAtChange = entity.Phase,
+            UserId = currentUser.UserId,
+            Summary = $"Điều chỉnh ngân sách: {diffSummary} {actorTag}",
+        });
+
+        await db.SaveChangesAsync(ct);
+    }
+}
+
 // ========== TRANSITION ==========
 
 public record TransitionPurchaseEvaluationCommand(