added 2 new root folders

shared-operations/functions/extractPages.js

@@ -0,0 +1,23 @@
+export async function extractPages(snapshot, pagesToExtractArray, PDFLib) {
+    const pdfDoc = await PDFLib.PDFDocument.load(snapshot)
+
+    // TODO: invent a better format for pagesToExtractArray and convert it.
+    return createSubDocument(pdfDoc, pagesToExtractArray, PDFLib);
+};
+
+export async function createSubDocument(pdfDoc, pagesToExtractArray, PDFLib) {
+    const subDocument = await PDFLib.PDFDocument.create();
+
+    // Check that array max number is not larger pdf pages number
+    if(Math.max(...pagesToExtractArray) >= pdfDoc.getPageCount()) {
+        throw new Error(`The PDF document only has ${pdfDoc.getPageCount()} pages and you tried to extract page ${Math.max(...pagesToExtractArray)}`);
+    }
+
+    const copiedPages = await subDocument.copyPages(pdfDoc, pagesToExtractArray);
+
+    for (let i = 0; i < copiedPages.length; i++) {
+        subDocument.addPage(copiedPages[i]);
+    }
+
+    return subDocument.save();
+}