How to combine multiple PDFs into one file.

Combining several PDFs is useful when an application, client or colleague expects one document instead of multiple attachments. The actual merge is simple, but a few preparation steps can prevent missing pages, the wrong order and an unnecessarily large final file.

Decide the final order before merging

Put the documents in the sequence the reader should see them. For an application, that might be a cover page followed by a form, supporting evidence and certificates. For a report, it may be the main document followed by appendices. Renaming local files with numbers such as 01, 02 and 03 can make the intended order easier to see before you select them.

Merge the files in the browser

Open the SizeFix Merge PDF tool, choose two or more PDFs and select them in the order you want them combined. The tool copies the pages into a new PDF rather than turning them into screenshots, so the page content is preserved during the merge.

Check the combined document

Open the downloaded PDF and scroll through every page. Confirm that the first and last pages are correct, the files appear in the expected order and no pages are missing or duplicated. If the document contains forms, links or selectable text, test the parts that matter before sending it.

What if the merged PDF becomes too large?

Merging does not normally reduce the size of the original page content, so the combined file may be roughly as large as all the source files together. If the final PDF exceeds an upload limit, use the PDF compressor after merging. For strict targets you can use the dedicated 200KB, 500KB or under-1MB compression pages.

If only some pages are required, it is usually better to remove unnecessary pages before compression. Use the Split PDF tool to extract the relevant pages instead of shrinking pages that the recipient does not need.

Avoid merging unrelated documents unnecessarily

A single combined file is useful when the destination specifically asks for one PDF. If separate documents need to be reviewed or signed independently, keeping them separate can be clearer. Follow the receiving website or organisation’s instructions rather than merging by default.

Privacy and local processing

The current SizeFix merger processes selected PDFs in the browser. That means the merge itself does not require a SizeFix server to receive and rebuild the pages. Browser processing also makes the tool responsive for normal-sized documents, although very large files can still use substantial memory on older phones.

Simple workflow

Prepare the files, confirm the order, merge them, open the output, check every page, and compress only if the final file exceeds the destination’s size limit. That sequence produces a cleaner result than repeatedly converting or re-saving PDFs without checking what changed.