Compare PDF

Put the old version of a document in the left box and the new version in the right box, then press the red button. A moment later you see a short summary, a list of every change with its page number, and both versions side by side with the differences coloured in. It works for contracts, reports, theses, price lists, manuals and any other file that went through more than one draft.

This is a quick way to compare pdf documents when someone sends back an edited file and you want to know exactly what they touched. You do not have to read both versions line by line, and you do not need the Word file the PDF was made from. The tool reads the PDFs themselves.

The tool reads the text of every page in both files and lines the words up from the first page to the last. It then works out the smallest set of words that has to be removed from the old version and added to the new one to turn one into the other. This is the same idea programmers use to see what changed between two versions of their code, a method known as the Myers diff.

Because the whole document is treated as one long stream of words, a new paragraph on page 2 that pushes the rest of the text down does not make every later page look different. The text that only moved is matched up again, and you see one change: the paragraph that was added. A simpler check that held page 1 against page 1 and page 2 against page 2 would flag everything after the insert as new.

Words that sit next to each other are grouped. A run of removed words followed straight away by added words becomes one changed item, so a reworded sentence shows as old text and new text together rather than as two separate entries. When you compare pdf for differences in a long contract, this keeps the list short and easy to read.

If two files are so different that thousands of words would have to change, the tool switches to a page by page comparison and says so next to the summary with the note Very different files: compared page by page. That usually means the files are not two versions of the same document, or that one of them was rebuilt from scratch with a new layout.

A word, for the tool, is any run of letters, numbers or marks between two spaces. So 1,500 and 1,800 are different words, 30 days and 60 days differ in one word, and a new e-mail address is one changed word. Hyphenated words such as long-term count as one word, which means that a removed hyphen shows up as a change.

Spaces, tabs and line breaks are never compared. A sentence that now breaks across two lines, a paragraph that wraps differently because the margins changed, or a double space typed by mistake does not appear in the list. That alone removes most of the noise you would get from checking two files by eye or with a plain text tool.

Numbers are compared exactly as they are written. 10.00 and 10 are different, and so are 5% and 5 %, because the second one has a space that splits it into two words. That strictness is useful for prices, quantities and dates, where one character can change the meaning of a whole clause.

Side by side is the view you see first. The page from the original is on the left and the same page number from the new version is on the right. Removed words are covered with a light red box on the left page, and added words with a light green box on the right page. A changed sentence therefore shows red on one side and green on the other.

The pages are drawn from the real PDF, so you see the layout, the fonts and the pictures exactly as they print, not a plain text copy. That makes it easy to compare pdf online side by side and check each change in its context: which clause it belongs to, which table row, which heading.

Both sides always show the same page number. If the new version has an extra page near the start, the matching text in the original may sit one page earlier. The list of changes gives the right page for each item, and the arrows let you step back or forward on both sides at once.

The word comparison only sees text. A swapped logo, a moved signature line, a new stamp, a changed chart or a different photo has no words in it, so the second view looks at pixels instead. Visual overlay draws the same page of both files at the same size and marks every pixel that looks different in red, over a faded copy of the new page.

Above the picture you see how much of the page changed, for example 0.84% of the page changed. A small number with a few red spots points to a small edit; a page that is mostly red usually means the content moved, for example because a paragraph was inserted above it. Use it to compare pdf for changes that the text list cannot show, such as formatting, colour, images and scanned pages.

The overlay holds a page against the page with the same number, so it works best when the two versions have the same layout. It is the right view for drawings, forms, certificates, designs and scans. For long text documents where paragraphs move, trust the word list and use the overlay to look at one page at a time.

The text comparison looks at the words only. If a word became bold, changed font, turned red or got bigger but kept the same spelling, it is not in the list of changes. These formatting-only changes are found by the visual overlay, which sees the page as a picture: a word that changed colour or weight shows up as red marks in the same place.

The same is true for new line spacing, wider margins, a moved image or a table with new borders. If the look matters, for example in a final print file or a branded template, step through the pages in Visual overlay after you have read the word list.

A scan is a photo of paper inside a PDF. It has no text the tool can read, so the word comparison has nothing to work with. If neither file has selectable text, a message says so and the tool switches to Visual overlay for you. If only one of the two has text, a note tells you that the overlay still shows its changes.

To compare the words of a scan, turn it into text first. Image to Text reads the words from a picture with OCR, and PDF to Text gets the text out of PDF pages. OCR is never perfect, so expect a few false changes where a letter was misread, and check those against the page before you act on them.

The visual overlay needs no text at all. For two scans of the same signed page, it shows where ink, stamps or handwriting differ, as long as both pages were scanned straight and at a similar size. A page scanned at a slight angle will light up red almost everywhere, so rescan it straight if you can.

Say a supplier sends back your contract with the note that they made a few small edits. Put the version you sent on Original (old) and their version on Changed (new). Leave both options off, so that every comma and capital counts, and start the comparison.

Read the summary first. A handful of changes means you can go through them one by one in a few minutes. Click each entry in the list: the page opens with the old wording in red on the left and the new wording in green on the right. Look closely at amounts, dates, notice periods, the names of the parties and words such as may, must, not and only, where a small edit can shift who has to do what.

Then switch to Visual overlay and step through the signature page and any page with a table or a logo, to be sure nothing outside the text was changed. Finally, download the ZIP. The CSV gives you a ready list to send back with your questions, and the two marked PDFs show your colleagues exactly where each change is.

Reports, theses and grant proposals often pass between several people, and not everyone uses tracked changes. When a co-author returns a PDF, put your last version on the left and theirs on the right. The list shows every sentence they rewrote, every paragraph they added and every reference they removed, each with its page number.

Tick Ignore upper / lower case if a style change turned headings into capitals, so those do not crowd the list. Keep the ZIP for each round of review. After a few rounds you have a clear record of who changed what and when, which helps when a supervisor asks why a section looks different from the draft they approved.

If the text moved because a new chapter was added near the start, the word comparison still lines up the rest of the document, so the list shows the new chapter and the real edits, not every page after it.

Long documents can have hundreds of changes. The list keeps them in reading order, from the first page to the last, so you can work through it from top to bottom without losing your place. Each entry shows the start of the old and new text; the full wording is on the page and in the CSV.

If most entries are small edits you do not care about, such as capitals in headings or tidied punctuation, tick the matching option and run the comparison again. The list gets shorter and the changes that matter stand out. For a team review, open changes.csv in a spreadsheet, add a column for who checks each row and a column for accept or reject, and share that sheet instead of the PDFs.

Press Marked PDFs + report (ZIP) and you get one file, pdf-comparison.zip. Inside are three files: a copy of the original with every removed word covered by a red box (its name ends in -removed-marked.pdf), a copy of the new version with every added word covered by a green box (-added-marked.pdf), and changes.csv.

The boxes are drawn on top of the page and are see-through, so the text under them can still be read, selected and searched. The marked copies are handy to send to a colleague or to keep with your records, because anyone can open them in a normal PDF reader without this website.

changes.csv is a plain table with one row per change: number, type, old page, new page, old text and new text. It opens in Excel, Google Sheets or Numbers, where you can sort, filter, add a column for comments or turn it into a review checklist. The button is greyed out when there is nothing to list.

There is no sign-up, no trial and no watermark on the marked copies. You open the page, add the two files and get the result. Because the work is done by your own device, there is no queue on a server and no daily limit, which is why you can compare pdf files online free as often as you like.

Speed depends on the size of the files and on your device. A few pages take a moment; a long report with hundreds of pages takes longer, because every word on every page is read before the comparison starts. A laptop or desktop is faster than an older phone for very large files.

Contracts, offers, salary letters and medical reports are not files you want to hand to a stranger's server. Here they are opened and compared inside your browser tab, by code that runs on your computer or phone. The PDFs are not uploaded and not stored by us, and closing the tab clears them from memory.

That is what lets you compare pdf files free online and secure at the same time: free because your device does the work, and secure because a file without a password never leaves it. Nothing is sent when you change an option, switch the view or download the ZIP either.

When a file needs a password to open, its box shows Password needed with a small field. Type the password and press Unlock. If it is wrong, you see That password did not open this PDF and can try again. Locked files up to 100 MB can be opened this way.

To remove the password, that one file is sent once over an encrypted connection to our server, and the unlocked copy comes straight back to your browser. The comparison itself still happens on your device. The marked copy in the ZIP download has no password; Protect PDF adds a new one if you need it, and Unlock PDF makes a copy without a password for good.

Desktop PDF editors that can compare files are often part of a paid plan, and installing software is not always allowed on a work computer. This page needs nothing but a modern browser such as Chrome, Edge, Firefox, Safari or Samsung Internet. That is all it takes to compare two pdf online, whether the files came from Word, Google Docs, a scanner app or a design program.

The two boxes are separate, so you can load each file from a different place: one from your Downloads folder and one straight from an e-mail attachment. Each box takes one PDF, by tapping Select PDF or by dropping the file on it.

On Windows and Mac, drag the old file from File Explorer or Finder onto Original (old) and the new one onto Changed (new). A large screen suits Side by side best, because both pages are big enough to read without zooming.

On iPhone and iPad, tap Select PDF and choose the file from the Files app, iCloud Drive or another storage app. On Android, the picker shows Downloads, Drive and other apps. The ZIP is saved to Downloads or Files, where you can open or share it. So you can compare pdfs free on whatever device you have with you.

On a small screen the two pages sit next to each other at a smaller size, so zoom in on a highlight or turn the phone sideways. The list of changes sits above the pages and stays easy to tap.

The word comparison reads the text layer of a PDF. Text that is part of a picture, such as a scan, a screenshot or a logo, is not read. Formatting such as bold, font, colour and size is not checked as text; use the visual overlay for that.

PDFs from some programs store text in an unusual order, for example in two columns, in tables or in text boxes placed by hand. The words are still compared, but a change may then look larger than it really is because the reading order differs. Special fonts can also make a word read slightly differently in the two files.

The overlay holds pages with the same number against each other and does not shift them to line up. If content moved down, much of the page turns red even though little changed. Pages that exist in only one file are not drawn in the overlay. Comments, bookmarks and attachments are not part of the text comparison.

Very large files take longer, because everything happens on your device. If the browser gets slow, cut a long file into parts with Split PDF and check the parts that matter most.

When you know what changed, you can act on it. Sign PDF adds your signature to the version you agree with, Merge PDF joins the final file with its attachments and Compress PDF makes it small enough for e-mail.

If you need to edit the words yourself, PDF to Word turns the PDF into a document you can change. To take out pages that should not be there, use Delete Pages, and Organize PDF puts the pages in a new order.