How to merge PDF files in the right order

Merging PDFs sounds trivial: take a few files and join them. In practice, the result is only useful if the pages end up in the right order, face the right way and contain what the recipient expects. A few minutes of planning saves you from sending a jumbled document and having to apologise for it.

Plan the order before you start

Before you open any tool, decide what the finished document should look like from the first page to the last. Think of it as a table of contents for a document that does not exist yet. A job application, for example, might be:

1. Cover letter
2. CV
3. Degree certificate
4. Reference letters, newest first

An expense claim might be the claim form first, followed by receipts in date order. A contract bundle might be the main agreement, then the annexes in the order they are numbered in the text. Whoever reads your file will usually go from top to bottom, so put the most important or most expected item first.

If the recipient gave instructions ("one PDF, form first, then supporting documents"), follow them exactly. Reviewers who handle many submissions often skim, and a missing or misplaced document can count against you.

Name your files so they sort themselves

Most merge tools add files in the order you select or upload them, and file pickers usually sort by name. You can use this to your advantage by giving your files names that sort correctly before you upload them:

• 01-cover-letter.pdf
• 02-cv.pdf
• 03-degree.pdf
• 04-reference-smith.pdf

Use leading zeros. Computers often sort text character by character, so without them 10-annex.pdf can appear before 2-annex.pdf. For dated items such as receipts or statements, put the date first in year-month-day format, for example 2026-03-14-hotel.pdf; that format sorts chronologically on its own.

Even if you can reorder files by dragging later, good names make it much easier to see at a glance whether everything is there.

Mixing images and PDFs

You will often need to combine PDFs with photos: a scanned form plus a phone photo of an ID card, or a report plus a picture of a receipt. Many merge tools accept JPG and PNG images directly and turn each image into a page. A few things to keep in mind:

• Page sizes may differ. An image page usually takes the proportions of the photo, so it may not be exactly the same size as your A4 or Letter pages. That is normal and does not cause problems for reading or printing.
• Crop before merging. A photo of a receipt on a kitchen table looks unprofessional. Crop it in your phone's photo editor first.
• Watch the file size. Phone photos are often several megabytes each. Ten of them can make the merged PDF too large to e-mail. See the section on file size below.

For more on turning photos into tidy pages, read turning phone photos and scans into a clean PDF.

Picking single pages from several files

You do not always want whole files. Maybe you need only the signature page of a contract, pages 3 to 5 of a long report and the first page of a certificate. You have two approaches:

• Extract first, then merge. Pull the pages you need out of each file into new, smaller PDFs, then merge those. This works with any toolset but takes several rounds.
• Merge with page-level selection. Some tools let you add individual pages from different files straight into the merge list, in any order. This is quicker and lets you interleave pages, for example page 1 of file A, then page 4 of file B, then page 2 of file A.

Interleaving is handy for things like combining a front-side scan and a back-side scan of a double-sided document, though for long documents it is a lot of clicking, so check carefully at the end.

Fixing rotations

Scans and phone photos are frequently sideways or upside down. Fix this before or during the merge, not after you have sent the file. When you rotate a page in a PDF, a good tool stores the rotation as a page setting rather than re-drawing the content, so no quality is lost.

Landscape pages, such as wide spreadsheets or charts, are a special case. They are not wrong, they are just wide. Leave them in landscape so they can be read without tilting your head, as long as their text runs left to right when you view them.

What can get lost when merging

Joining PDFs copies the visible content of the pages reliably. Some extra features are more fragile:

• Bookmarks (the outline). The clickable chapter list in the side panel of a PDF reader may not carry over, or may be lost entirely.
• Form fields. Fillable forms can lose their interactive fields, or fields with the same name in different files can interfere with each other. If a form must stay fillable, send it as a separate file. If it is already filled in, printing it to PDF first (many systems offer a "Print to PDF" option) is a common way to make the entries a permanent part of the page.
• Digital signatures. A digitally signed PDF is sealed. Any change, including merging it with other files, invalidates the signature. If a signed document must stay verifiable, send it on its own, alongside the merged file.
• Links. Links within a document may stop working; links to websites usually survive but not always.

The printed appearance of each page stays the same. It is the "clickable" layer that may suffer.

File size after merging

A merged PDF is roughly the sum of its parts. If you join a 4 MB scan, a 6 MB scan and three phone photos at 3 MB each, expect around 19 MB. Sometimes the result is a little smaller, because shared fonts may be stored once; sometimes slightly bigger.

If the merged file is too large to send, compress it afterwards. A medium compression level is usually enough for scans and photos to shrink substantially while staying readable. The guide how to reduce a PDF's file size explains how to choose a level.

Check before you send

1. Scroll through the merged PDF from start to finish.
2. Confirm the page count matches what you expected.
3. Check that every page faces the right way.
4. Make sure nothing is duplicated and nothing is missing.
5. Give the file a clear name, such as application-jane-doe.pdf, rather than merged.pdf.

Doing it on FlexyFiles

On FlexyFiles you can merge whole files and single pages, from different files and in any order, and mix in JPG and PNG images.

1. Open Merge PDF and upload your PDFs and images. They appear under "Your files".
2. To merge whole files, use "Add whole file" for each one (click "Open full workspace" if you want the three-column view with the large preview). To pick single pages, click the + next to a file to open its page list, select a page and choose "Add this page" under the large preview.
3. In the "Processing" panel, drag items to reorder them, rotate any that are sideways, and remove anything added by mistake.
4. Type a name under "Save as" and click Run. The merged PDF appears in "Your files", ready to download. Your original files are not changed.

In the full workspace at /pdf/app, you can chain further steps after the merge, for example Merge, then Compress, then Add page numbers, and get one finished file. If you need to rearrange pages inside an existing PDF instead, use Organize PDF, explained in our guide to organizing PDF pages.