Merging PDFs comes up whenever you need to file invoices and receipts by month, read a document that arrived split across chapters, or submit an application as a single file. The task itself is trivial. What is not trivial is deciding whether a contract or a certificate should be uploaded to somebody else's merge service just to get it done.
OFFiler removes that decision. When you open this page, the code that performs the merge is loaded into your browser, and from then on the PDFs you pick are read and written entirely in your device's memory. Neither the contents nor the filenames are transmitted anywhere. Below is what actually happens inside, what survives the merge and what does not, and which tools are worth chaining before or after it.
What happens inside
Pages are copied, not re-encoded
The merge runs on pdf-lib. It creates one empty PDF document, then copies every page of each selected file into it. Page contents — text drawing operators, embedded fonts, placed images — are copied as objects. Nothing is re-compressed and nothing is re-rendered.
As a result, text stays sharp and stays selectable and searchable after merging. The side effects you get from tools that flatten pages into images — blurry glyphs, text you can no longer copy — do not happen here. The output size lands close to the sum of the inputs.
Order is whatever you drag it to be
Added PDFs appear as thumbnails you can drag to reorder, and the merge follows that on-screen order exactly. You do not need to rename files to "01_", "02_" just to control the sequence. Multiple files can be selected at once.
What does not carry over
Bookmarks and document metadata are not carried over
What gets copied is the pages. Bookmarks (the outline tree) belong to the document as a whole, so they do not survive into the merged file. For the same reason the original title, author, and creation date do not carry over — the output PDF has those fields empty.
PDFs containing fillable form fields may also stop being fillable after a merge, because the form definition is held at document level. If you only need to reorder pages while keeping bookmarks and form fields intact, use the page organizer instead of merging.
Password-protected PDFs cannot be merged directly
A PDF that requires a password to open will fail at the load step: its contents are encrypted, and pages cannot be copied without decrypting them first. If you know the password, remove the protection with the unlock tool first, then merge.
Speed is bounded by your device, not by a queue
Not sending files to a server also means the computation happens on the device in front of you. The tool is sized for files up to 100 MB each; merging several hundred-page PDFs at once can take a while on a modest machine. In exchange there is no queue and no daily processing cap.
Chaining before and after
Trim first, then merge
When the goal is "pull the pages I need out of several documents and combine them", extract or delete pages first, then merge. OFFiler lets you hand the result of one tool straight to the next without saving and re-uploading in between, so extract → merge runs as one flow.
Shrink or redact afterwards
If the merged file is too large for an email attachment, pass it to PDF compression; if parts of it need to be hidden before it leaves the company, pass it to markup. Compression offers a mode that only strips metadata, so you can reduce size without destroying the selectable text the merge preserved.
Specs and limits
- Input format
- PDF (application/pdf)
- Size limit
- 100 MB per file
- Number of files
- No fixed cap — bounded by device memory
- Quality
- No re-encoding; text stays selectable and searchable
- Not carried over
- Bookmarks, document metadata, fillable form fields
- Encrypted PDFs
- Not supported — unlock first
- Network
- No file upload; all processing in-browser