diff --git a/feature/pdf/src/commonMain/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapper.kt b/feature/pdf/src/commonMain/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapper.kt
index e8c88c1b41..79c96b2b6b 100644
--- a/feature/pdf/src/commonMain/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapper.kt
+++ b/feature/pdf/src/commonMain/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapper.kt
@@ -65,15 +65,13 @@ class LoiReportMapper(
           ),
         mapBlock = buildMapBlock(details),
       )
-    val dateMillis = submission.lastModified.clientTimestamp
-    val timestamp =
-      "${dateFormatter.formatDate(dateMillis)}_${dateFormatter.formatTime(dateMillis)}"
+
     val fileName =
-      listOf(details.surveyName, loiReport.loiName, details.userName, timestamp)
+      listOf(details.surveyName, loiReport.loiName, details.userName)
         .map { it.filter(::isSafeFileChar) }
         .filter { it.isNotBlank() }
         .joinToString("_")
-        .take(100)
+        .take(60) + "_${submission.id}"
 
     return PdfExportService.Request(
       document = document,
diff --git a/feature/pdf/src/commonTest/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapperTest.kt b/feature/pdf/src/commonTest/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapperTest.kt
index 3b8bbc73fb..e0b504291f 100644
--- a/feature/pdf/src/commonTest/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapperTest.kt
+++ b/feature/pdf/src/commonTest/kotlin/org/groundplatform/feature/pdf/mapper/LoiReportMapperTest.kt
@@ -18,6 +18,7 @@ package org.groundplatform.feature.pdf.mapper
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertNull
+import kotlin.test.assertTrue
 import kotlinx.coroutines.test.runTest
 import org.groundplatform.domain.model.geometry.Coordinates
 import org.groundplatform.domain.model.geometry.LinearRing
@@ -46,7 +47,7 @@ class LoiReportMapperTest {
     )
 
   @Test
-  fun `file name joins survey loi user and timestamp with underscores`() = runTest {
+  fun `file name joins survey loi user and submission id with underscores`() = runTest {
     val request =
       mapper.map(
         loiReport =
@@ -58,7 +59,7 @@ class LoiReportMapperTest {
         submission = submission,
       )
 
-    assertEquals("Survey_Loi_User_$TEST_TIMESTAMP", request!!.fileName)
+    assertEquals("Survey_Loi_User_$TEST_SUBMISSION_ID", request!!.fileName)
   }
 
   @Test
@@ -77,7 +78,7 @@ class LoiReportMapperTest {
         submission = submission,
       )
 
-    assertEquals("MySurvey_loiname_useremailcom_$TEST_TIMESTAMP", request!!.fileName)
+    assertEquals("MySurvey_loiname_useremailcom_$TEST_SUBMISSION_ID", request!!.fileName)
   }
 
   @Test
@@ -93,7 +94,7 @@ class LoiReportMapperTest {
         submission = submission,
       )
 
-    assertEquals("loi_$TEST_TIMESTAMP", request!!.fileName)
+    assertEquals("loi_$TEST_SUBMISSION_ID", request!!.fileName)
   }
 
   @Test
@@ -109,7 +110,7 @@ class LoiReportMapperTest {
         submission = submission,
       )
 
-    assertEquals("แบบสำรวจ_ເພີ່ມຈຸດສຳຫຼວດ_テスト_$TEST_TIMESTAMP", request!!.fileName)
+    assertEquals("แบบสำรวจ_ເພີ່ມຈຸດສຳຫຼວດ_テスト_$TEST_SUBMISSION_ID", request!!.fileName)
   }
 
   @Test
@@ -128,11 +129,11 @@ class LoiReportMapperTest {
         submission = submission,
       )
 
-    assertEquals("CaféSãoJosé_ß_Test_$TEST_TIMESTAMP", request!!.fileName)
+    assertEquals("CaféSãoJosé_ß_Test_$TEST_SUBMISSION_ID", request!!.fileName)
   }
 
   @Test
-  fun `file name is capped at 100 characters`() = runTest {
+  fun `file name is capped at 60 characters and still ends with the submission id`() = runTest {
     val request =
       mapper.map(
         loiReport =
@@ -144,26 +145,58 @@ class LoiReportMapperTest {
         submission = submission,
       )
 
-    assertEquals(100, request!!.fileName.length)
+    val fileName = request!!.fileName
+    assertEquals(60, fileName.removeSuffix("_$TEST_SUBMISSION_ID").length)
+    assertTrue(fileName.endsWith("_$TEST_SUBMISSION_ID"))
   }
 
   @Test
-  fun `timestamp comes from the submission's own last modified date`() = runTest {
+  fun `file name stays within the file system byte limit for multi-byte scripts`() = runTest {
     val request =
       mapper.map(
         loiReport =
           FakeDataGenerator.newLoiReport(
-            loiName = "Loi",
+            loiName = "ເພີ່ມຈຸດສຳຫຼວດ".repeat(20),
             submissionDetails =
-              FakeDataGenerator.newSubmissionDetails(surveyName = "Survey", userName = "User"),
+              FakeDataGenerator.newSubmissionDetails(
+                surveyName = "แบบสำรวจ".repeat(20),
+                userName = "テスト".repeat(20),
+              ),
           ),
+        submission = submission,
+      )
+
+    assertTrue(request!!.fileName.encodeToByteArray().size <= 255)
+  }
+
+  @Test
+  fun `submissions sharing survey, loi name and user get different file names`() = runTest {
+    val loiReport =
+      FakeDataGenerator.newLoiReport(
+        loiName = "Loi",
+        submissionDetails =
+          FakeDataGenerator.newSubmissionDetails(surveyName = "Survey", userName = "User"),
+      )
+
+    val first = mapper.map(loiReport, FakeDataGenerator.newSubmission(id = "a"))
+    val second = mapper.map(loiReport, FakeDataGenerator.newSubmission(id = "b"))
+
+    assertEquals("Survey_Loi_User_a", first!!.fileName)
+    assertEquals("Survey_Loi_User_b", second!!.fileName)
+  }
+
+  @Test
+  fun `header timestamp comes from the submission's own last modified date`() = runTest {
+    val request =
+      mapper.map(
+        loiReport = FakeDataGenerator.newLoiReport(),
         submission =
           FakeDataGenerator.newSubmission(
             lastModified = AuditInfo(FakeDataGenerator.newUser(), clientTimestamp = 42L)
           ),
       )
 
-    assertEquals("Survey_Loi_User_DATE42_TIME42", request!!.fileName)
+    assertEquals("DATE(42) TIME(42)", request!!.document.header.timestamp)
   }
 
   @Test
@@ -286,11 +319,11 @@ class LoiReportMapperTest {
           )
         )
       )
-    const val TEST_TIMESTAMP = "DATE0_TIME0"
-    /** Submission with a fixed last-modified timestamp so date assertions are deterministic. */
+    const val TEST_SUBMISSION_ID = "submissionId"
     val submission =
       FakeDataGenerator.newSubmission(
-        lastModified = AuditInfo(FakeDataGenerator.newUser(), clientTimestamp = 0L)
+        id = TEST_SUBMISSION_ID,
+        lastModified = AuditInfo(FakeDataGenerator.newUser(), clientTimestamp = 0L),
       )
   }
 }