Compare PDF: guide, privacy and troubleshooting
Compare PDF is designed for a specific document workflow: compare pdf files online free — side by side. The best results start with a source file that opens correctly and has the pages or content you actually want to process. Before you begin, check that you selected the right document, confirm its orientation and page count, and keep an untouched copy if the file is important. This is especially useful for invoices, reports, application forms, study material and other documents where a small conversion difference can matter.
How to use Compare PDF
- Choose the two PDF versions you want to compare — in that order.
- Press “Compare PDFs”; each output page shows one page of each file next to each other.
- Download the comparison PDF and read across the dashed line.
After the tool finishes, download the result and open it in the application where you plan to use it. Check page order, headings, tables, symbols, images and any fields that matter to your workflow. PDF is a fixed-layout format, while formats such as Word and Excel represent content differently; conversions can therefore need a small manual correction. Scanned pages also behave differently from digital PDFs because the page may contain an image rather than selectable text. When a result does not look right, try a clearer source scan, a smaller batch, or the related tool linked on this page.
Privacy and local processing
PDFKaj's client-side tools process document content in your browser instead of uploading it to a PDFKaj document-processing server. The browser downloads the application code and any required libraries, then uses your device to read the selected file and prepare the output. Your original file remains unchanged; the generated file is offered for download. Some tools need an internet connection the first time they load code or language data, and the optional AI document assistant is different: it can send extracted text to OpenAI only after you provide a key and explicitly consent. Read the Privacy Policy for the details and exceptions.
Performance and troubleshooting
Processing takes memory as well as time. Large PDFs, high-resolution scans and documents with hundreds of pages may use substantial RAM, especially on phones or older laptops. If the browser becomes slow, close other tabs, try a smaller file, split a long PDF into sections, or use a device with more available memory. Keep the tab open until the download finishes. A failed conversion does not mean the source file was changed; retry with a copy and check whether the PDF is password-protected, damaged or unusually complex.
Large-file performance notice
Frequently asked questions
Which file is on which side?
The first file you picked is on the left, the second on the right, and every page is labelled with its file name.
What if the files have a different number of pages?
The comparison runs to the longer document, and the missing side is simply left blank.
Does it highlight the differences?
No — it puts the pages side by side so your eye catches what changed. It does not rewrite a single line of either document.