diff --git a/CHANGELOG.md b/CHANGELOG.md
index f38b747d5..ac4d2054d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # Change Log
 
+- docs api: added the Checking PDF forms page
 - docspace backend: added the Removed user page
 
 ## 6.3.0
diff --git a/site/pages/Docs/Docs API/Get Started/How It Works/Checking PDF forms/index.md b/site/pages/Docs/Docs API/Get Started/How It Works/Checking PDF forms/index.md
new file mode 100644
index 000000000..65d0f40a2
--- /dev/null
+++ b/site/pages/Docs/Docs API/Get Started/How It Works/Checking PDF forms/index.md	
@@ -0,0 +1,239 @@
+---
+order: -1
+---
+
+PDF forms differ from standard PDF files in form metadata. It determines which editor opens a file: the form editor or the standard PDF editor.
+
+To distinguish standard PDF files from PDF forms, you can use the check functions. These functions take the first 300 bytes of the file and check if there is `"ONLYOFFICEFORM"` there. If `true`, then it is an extended PDF file. Otherwise, it is a standard PDF file.
+
+Below you can find the check functions in different programming languages. 
+
+## JavaScript
+
+```ts
+function isExtendedPDFFile(text) {
+  if (!text) {
+    return false
+  }
+  const indexFirst = text.indexOf("%\u00CD\u00CA\u00D2\u00A9\u000D")
+  if (indexFirst === -1) {
+    return false
+  }
+  let pFirst = text.slice(indexFirst + 6)
+  if (!(pFirst.lastIndexOf("1 0 obj\u000A<<\u000A", 0) === 0)) {
+    return false
+  }
+  pFirst = pFirst.slice(11)
+  const signature = "ONLYOFFICEFORM"
+  const indexStream = pFirst.indexOf("stream\u000D\u000A")
+  const indexMeta = pFirst.indexOf(signature)
+  if (indexStream === -1 || indexMeta === -1 || indexStream < indexMeta) {
+    return false
+  }
+  let pMeta = pFirst.slice(indexMeta)
+  pMeta = pMeta.slice(signature.length + 3)
+  let indexMetaLast = pMeta.indexOf(" ")
+  if (indexMetaLast === -1) {
+    return false
+  }
+  pMeta = pMeta.slice(indexMetaLast + 1)
+  indexMetaLast = pMeta.indexOf(" ")
+  if (indexMetaLast === -1) {
+    return false
+  }
+  return true
+}
+```
+
+## Node.js
+
+```ts
+DocManager.prototype.isExtendedPDFFile = function isExtendedPDFFile(fileName) {
+  let filePath = this.forcesavePath(fileName, null, false)
+  if (filePath === "") {
+    filePath = this.storagePath(fileName)
+  }
+  const bufferSize = 300
+  const buffer = Buffer.alloc(bufferSize)
+  const fd = fileSystem.openSync(filePath, "r")
+  fileSystem.readSync(fd, buffer, 0, bufferSize)
+  fileSystem.closeSync(fd)
+  const pBuffer = buffer.toString("latin1")
+  const indexFirst = pBuffer.indexOf("%\u00CD\u00CA\u00D2\u00A9\u000D")
+  if (indexFirst === -1) {
+    return false
+  }
+  let pFirst = pBuffer.slice(indexFirst + 6)
+  if (!pFirst.startsWith("1 0 obj\u000A<<\u000A")) {
+    return false
+  }
+  pFirst = pFirst.slice(11)
+  const indexStream = pFirst.indexOf("stream\u000D\u000A")
+  const indexMeta = pFirst.indexOf(configServer.get("gFormatOformPdfMetaTag"))
+  if (indexStream === -1 || indexMeta === -1 || indexStream < indexMeta) {
+    return false
+  }
+  let pMeta = pFirst.slice(indexMeta)
+  pMeta = pMeta.slice(configServer.get("gFormatOformPdfMetaTag").length + 3)
+  let indexMetaLast = pMeta.indexOf(" ")
+  if (indexMetaLast === -1) {
+    return false
+  }
+  pMeta = pMeta.slice(indexMetaLast + 1)
+  indexMetaLast = pMeta.indexOf(" ")
+  if (indexMetaLast === -1) {
+    return false
+  }
+  return true
+}
+```
+
+## Java Spring
+
+```java
+@SneakyThrows
+public Boolean isExtendedPDFFile(final String fileName) {
+  Resource resource = storageMutator.loadFileAsResource(fileName);
+  byte[] bytes;
+  try (InputStream inputStream = resource.getInputStream()) {
+    bytes = inputStream.readNBytes(110);
+  } catch (Exception e) {
+    return false;
+  }
+  String pBuffer = new String(bytes, "Windows-1252");
+  int indexFirst = pBuffer.indexOf("%\315\312\322\251\015");
+  if (indexFirst == -1) {
+    return false;
+  }
+  String pFirst = pBuffer.substring(indexFirst + 6);
+  if (!pFirst.startsWith("1 0 obj\012<<\012")) {
+    return false;
+  }
+  pFirst = pFirst.substring(11);
+  int indexStream = pFirst.indexOf("stream\015\012");
+  int indexMeta = pFirst.indexOf(Constants.G_FORMAT_OFORM_PDF_META_TAG);
+  if (indexStream == -1 || indexMeta == -1 || indexStream < indexMeta) {
+    return false;
+  }
+  String pMeta = pFirst.substring(indexMeta);
+  pMeta = pMeta.substring(Constants.G_FORMAT_OFORM_PDF_META_TAG.length() + 3);
+  int indexMetaLast = pMeta.indexOf(" ");
+  if (indexMetaLast == -1) {
+    return false;
+  }
+  pMeta = pMeta.substring(indexMetaLast + 1);
+  indexMetaLast = pMeta.indexOf(" ");
+  if (indexMetaLast == -1) {
+    return false;
+  }
+  return true;
+}
+```
+
+## C++
+
+```cpp
+bool COfficeFileFormatChecker::isPdfOformFormatFile(unsigned char *pBuffer, int dwBytes)
+{
+  pBuffer[dwBytes - 1] = 0;
+  char* pFirst = strstr((char*)pBuffer, "%\315\312\322\251\015");
+  if (!pFirst || pFirst - (char*)pBuffer + 6 >= dwBytes)
+    return false;
+  pFirst += 6;
+  if (strncmp(pFirst, "1 0 obj\012<<\012", 11) != 0 || pFirst - (char*)pBuffer + 11 >= dwBytes)
+    return false;
+  pFirst += 11;
+  char* pStream = strstr(pFirst, "stream\015\012");
+  char* pMeta = strstr(pFirst, g_format_oform_pdf_meta_tag);
+  if (!pStream || !pMeta || pStream < pMeta)
+    return false;
+  pMeta += strlen(g_format_oform_pdf_meta_tag) + 3;
+  char* pMetaLast = strstr(pMeta, " ");
+  if (!pMetaLast)
+    return false;
+  pMeta = pMetaLast + 1;
+  pMetaLast = strstr(pMeta, " ");
+  if (!pMetaLast)
+    return false;
+  return true;
+}
+```
+
+## Python
+
+```py
+def is_pdf_form(text):
+  if not text:
+    return False
+    
+  index_first = text.find(b"%\xCD\xCA\xD2\xA9\x0D")
+  if index_first == -1:
+    return False
+    
+  p_first = text[index_first + 6:]
+  if not p_first.startswith(b"1 0 obj\x0A<<\x0A"):
+    return False
+    
+  p_first = p_first[11:]
+  signature = b"ONLYOFFICEFORM"
+  index_stream = p_first.find(b"stream\x0D\x0A")
+  index_meta = p_first.find(signature)
+  if index_stream == -1 or index_meta == -1 or index_stream < index_meta:
+    return False
+    
+  p_meta = p_first[index_meta:]
+  p_meta = p_meta[len(signature) + 3:]
+  index_meta_last = p_meta.find(b" ")
+  if index_meta_last == -1:
+    return False
+    
+  p_meta = p_meta[index_meta_last + 1:]
+  index_meta_last = p_meta.find(b" ")
+  if index_meta_last == -1:
+    return False
+    
+  return True
+```
+
+## PHP
+
+```php
+<?php
+
+public function isOnlyofficeForm($file) {
+  if ($file === null) return false;
+ 
+  $limitDetect = 300;
+  $onlyofficeFormMetaTag = "ONLYOFFICEFORM";
+  $path = $file->getStoredFilePath() . "file";
+  $content = file_get_contents($path, false, null, 0, $limitDetect);
+  $indexFirst = strpos($content, "%\xCD\xCA\xD2\xA9\x0D");
+  if ($indexFirst === false) {
+    return false;
+  }
+  $pFirst = substr($content, $indexFirst + 6);
+  if (!str_starts_with($pFirst, "1 0 obj\n<<\n")) {
+    return false;
+  }
+  $pFirst = substr($pFirst, 11);
+  $indexStream = strpos($pFirst, "stream\x0D\x0A");
+  $indexMeta = strpos($pFirst, $onlyofficeFormMetaTag);
+  if ($indexStream === false || $indexMeta === false || $indexStream < $indexMeta) {
+    return false;
+  }
+  $pMeta = substr($pFirst, $indexMeta);
+  $pMeta = substr($pMeta, strlen($onlyofficeFormMetaTag) + 3);
+  $indexMetaLast = strpos($pMeta, " ");
+  if ($indexMetaLast === false) {
+    return false;
+  }
+  $pMeta = substr($pMeta, $indexMetaLast + 1);
+  $indexMetaLast = strpos($pMeta, " ");
+  if ($indexMetaLast === false) {
+    return false;
+  }
+  return true;
+}
+
+?>
+```
diff --git a/site/pages/Docs/Docs API/Get Started/How It Works/Setting avatars/index.md b/site/pages/Docs/Docs API/Get Started/How It Works/Setting avatars/index.md
index 040114dbd..5db1dc993 100644
--- a/site/pages/Docs/Docs API/Get Started/How It Works/Setting avatars/index.md	
+++ b/site/pages/Docs/Docs API/Get Started/How It Works/Setting avatars/index.md	
@@ -1,5 +1,5 @@
 ---
-order: -1
+order: -2
 ---
 
 The reference figure and the steps below explain the process of setting the avatars for the users in ONLYOFFICE Docs.
diff --git a/site/pages/Docs/Docs API/Get Started/How It Works/index.md b/site/pages/Docs/Docs API/Get Started/How It Works/index.md
index 1c47fc920..be371fab8 100644
--- a/site/pages/Docs/Docs API/Get Started/How It Works/index.md	
+++ b/site/pages/Docs/Docs API/Get Started/How It Works/index.md	
@@ -26,6 +26,7 @@ In this section you will learn how to:
 - [Embedding forms into a web page](Embedding%20forms%20into%20a%20web%20page/index.md)
 - [Protecting ranges](Protecting%20ranges/index.md)
 - [Setting avatars](Setting%20avatars/index.md)
+- [Checking PDF forms](Checking%20PDF%20forms/index.md)
 
 ## User-document interaction