Fix PDF import with libreoffice (#4156)

Fix #4151

src/node/utils/LibreOffice.js

@@ -44,6 +44,10 @@ exports.convertFile = function(srcFile, destFile, type, callback) {
   if (type === "html") {
     // "html:XHTML Writer File:UTF8" does a better job than normal html exports
     type = "html:XHTML Writer File:UTF8";
+    // PDF files need to be converted with LO Draw ref https://github.com/ether/etherpad-lite/issues/4151
+    if (path.extname(srcFile).toLowerCase() === ".pdf") {
+      type = "html:XHTML Draw File"
+    }
   }
 
   // soffice can't convert from html to doc directly (verified with LO 5 and 6)