Best Free Online Tool for PDF Merger – Secure & Fast

(function(){ // ———- File storage ———- let pdfFilesQueue = []; // each item: { id, file, name, size } let nextId = 1; // DOM references const dropZone = document.getElementById(‘dropZone’); const fileInput = document.getElementById(‘fileInput’); const selectBtn = document.getElementById(‘selectFilesBtn’); const fileListContainer = document.getElementById(‘fileListContainer’); const mergeBtn = document.getElementById(‘mergeBtn’); const resetBtn = document.getElementById(‘resetBtn’); const clearAllBtn = document.getElementById(‘clearAllBtn’); const statusContainer = document.getElementById(‘statusContainer’); // render file list UI function renderFileList() { if (!fileListContainer) return; if (pdfFilesQueue.length === 0) { fileListContainer.innerHTML = ‘

No files added. Add PDF files to start merging.

‘; return; } let html = ”; pdfFilesQueue.forEach((item, idx) => { const sizeMB = (item.size / 1024 / 1024).toFixed(2); const sizeDisplay = sizeMB >= 1 ? `${sizeMB} MB` : `${(item.size / 1024).toFixed(0)} KB`; html += `

${escapeHtml(item.name)} ${sizeDisplay}

`; }); fileListContainer.innerHTML = html; // attach event handlers for dynamic buttons document.querySelectorAll(‘.btn-move-up’).forEach(btn => { btn.addEventListener(‘click’, (e) => { e.stopPropagation(); const id = parseInt(btn.getAttribute(‘data-id’)); moveFileUp(id); }); }); document.querySelectorAll(‘.btn-move-down’).forEach(btn => { btn.addEventListener(‘click’, (e) => { e.stopPropagation(); const id = parseInt(btn.getAttribute(‘data-id’)); moveFileDown(id); }); }); document.querySelectorAll(‘.btn-remove’).forEach(btn => { btn.addEventListener(‘click’, (e) => { e.stopPropagation(); const id = parseInt(btn.getAttribute(‘data-id’)); removeFileById(id); }); }); } // helper functions function escapeHtml(str) { if(!str) return ”; return str.replace(/[&]/g, function(m) { if(m === ‘&’) return ‘&’; if(m === ”) return ‘>’; return m; }); } function moveFileUp(id) { const index = pdfFilesQueue.findIndex(f => f.id === id); if(index > 0) { [pdfFilesQueue[index-1], pdfFilesQueue[index]] = [pdfFilesQueue[index], pdfFilesQueue[index-1]]; renderFileList(); } } function moveFileDown(id) { const index = pdfFilesQueue.findIndex(f => f.id === id); if(index !== -1 && index f.id !== id); renderFileList(); clearStatus(); } function clearAllFiles() { pdfFilesQueue = []; renderFileList(); clearStatus(); } function clearStatus() { if(statusContainer) statusContainer.innerHTML = ”; } // add new files (avoid exact duplicates) function addFiles(files) { if(!files || files.length === 0) return; let addedCount = 0; for(let file of files) { if(file.type !== ‘application/pdf’) { showTemporaryError(`File “${file.name}” is not a PDF, skipped.`); continue; } const isDuplicate = pdfFilesQueue.some(f => f.name === file.name && f.size === file.size); if(isDuplicate) { showTemporaryError(`⚠️ File “${file.name}” already exists in the list, duplicate ignored.`); continue; } pdfFilesQueue.push({ id: nextId++, file: file, name: file.name, size: file.size }); addedCount++; } if(addedCount > 0) { renderFileList(); clearStatus(); } } function showTemporaryError(msg) { const existing = statusContainer.querySelector(‘.temp-error’); if(existing) existing.remove(); const errDiv = document.createElement(‘div’); errDiv.className = ‘error-card temp-error’; errDiv.style.padding = ’15px’; errDiv.style.marginTop = ’10px’; errDiv.innerHTML = ` ${msg}`; statusContainer.prepend(errDiv); setTimeout(() => { if(errDiv && errDiv.remove) errDiv.remove(); }, 3000); } // —– merge process using pdf-lib (100% client side) —– async function startMerge() { if(pdfFilesQueue.length === 0) { showTemporaryError(‘No files to merge. Please add PDF files first.’); return; } if(pdfFilesQueue.length === 1) { showTemporaryError(‘You need at least two PDF files to merge. Add more files.’); return; } // disable buttons during processing mergeBtn.disabled = true; resetBtn.disabled = true; clearAllBtn.disabled = true; // show progress UI statusContainer.innerHTML = ` `; const progressText = document.getElementById(‘mergeProgressText’); try { const mergedPdf = await PDFLib.PDFDocument.create(); let totalFiles = pdfFilesQueue.length; for(let i = 0; i mergedPdf.addPage(page)); } if(progressText) progressText.innerText = ‘Generating final PDF file…’; const mergedPdfBytes = await mergedPdf.save(); const blob = new Blob([mergedPdfBytes], { type: ‘application/pdf’ }); const downloadUrl = URL.createObjectURL(blob); const timestamp = new Date().toISOString().slice(0,19).replace(/:/g, ‘-‘); const fileName = `merged_docs_${timestamp}.pdf`; statusContainer.innerHTML = ` `; const downloadLinkEl = document.getElementById(‘finalDownloadLink’); if(downloadLinkEl) { downloadLinkEl.addEventListener(‘click’, (e) => { // allow download naturally }); } const newMergeBtn = document.getElementById(‘newMergeReset’); if(newMergeBtn) { newMergeBtn.addEventListener(‘click’, () => { URL.revokeObjectURL(downloadUrl); resetAllState(); }); } } catch (err) { console.error(err); statusContainer.innerHTML = ` `; const tryAgain = document.getElementById(‘tryAgainReset’); if(tryAgain) tryAgain.addEventListener(‘click’, () => resetAllState()); } finally { mergeBtn.disabled = false; resetBtn.disabled = false; clearAllBtn.disabled = false; } } // read file as ArrayBuffer using Promise function readFileAsArrayBuffer(file) { return new Promise((resolve, reject) => { const reader = new FileReader(); reader.onload = () => resolve(reader.result); reader.onerror = () => reject(new Error(`Failed to read file: ${file.name}`)); reader.readAsArrayBuffer(file); }); } function resetAllState() { pdfFilesQueue = []; nextId = 1; renderFileList(); clearStatus(); mergeBtn.disabled = false; resetBtn.disabled = false; clearAllBtn.disabled = false; } // drag & drop setup function setupDragAndDrop() { dropZone.addEventListener(‘dragover’, (e) => { e.preventDefault(); dropZone.classList.add(‘drag-over’); }); dropZone.addEventListener(‘dragleave’, () => { dropZone.classList.remove(‘drag-over’); }); dropZone.addEventListener(‘drop’, (e) => { e.preventDefault(); dropZone.classList.remove(‘drag-over’); const items = e.dataTransfer.files; if(items && items.length) { addFiles(Array.from(items)); } }); dropZone.addEventListener(‘click’, (e) => { if(e.target === dropZone || e.target.closest(‘.drop-area’) && !e.target.closest(‘#selectFilesBtn’)) { fileInput.click(); } }); } // initialize all event listeners function init() { setupDragAndDrop(); selectBtn.addEventListener(‘click’, (e) => { e.stopPropagation(); fileInput.click(); }); fileInput.addEventListener(‘change’, (e) => { if(e.target.files && e.target.files.length) { addFiles(Array.from(e.target.files)); } fileInput.value = ”; }); mergeBtn.addEventListener(‘click’, startMerge); resetBtn.addEventListener(‘click’, resetAllState); clearAllBtn.addEventListener(‘click’, clearAllFiles); renderFileList(); } init(); })();

💡 Technical Specifications & Document Security

All your files are processed completely locally inside your browser using advanced JavaScript and WebAssembly frameworks. No documents are uploaded to our servers, ensuring 100% privacy and global data security compliance.