Client needed all their monthly reports combined into one PDF. Simple request, right? Just merge 12 PDFs together.
Except I'd never actually done this before. Figured there'd be free tools online. There were. Like, hundreds of them. Which one should I use?
Instead of just picking randomly, I decided to test a bunch. Used the same 12 PDFs for each test. Documented what worked, what didn't, and which tools I'd actually use again.
This is what I found.
The Test Setup
My 12 test PDFs included:
- 3 reports with graphs and charts (each around 5MB)
- 4 text-heavy documents (1-2MB each)
- 2 PDFs with embedded images (8MB and 12MB)
- 2 forms with fillable fields
- 1 PDF that was password-protected (wanted to see how tools handled this)
Total size: about 45MB
I tested each tool for:
- How easy it was to use
- Quality of the merged result
- File size of the output
- Whether it preserved formatting, images, fonts
- Speed
- Hidden costs or limitations
Tool #1: Smallpdf (Online)
First Impression: Clean interface, drag-and-drop worked smoothly
The Process: Uploaded all 12 files, dragged them into the order I wanted, clicked "Merge PDF."
Results:
- Output: 44.2MB (close to original size)
- Quality: Perfect - no visible degradation
- Speed: About 45 seconds
- Issues: Free version limits you to 2 operations per day. I hit that limit immediately because I was testing multiple tools.
Verdict: Works great for occasional use. The daily limit is annoying if you need to merge multiple sets of PDFs.
Tool #2: iLovePDF (Online)
First Impression: Very similar to Smallpdf, slightly busier interface
The Process: Same drag-and-drop approach. Also offers batch file upload which saved time.
Results:
- Output: 42.8MB (actually smaller than original)
- Quality: Excellent
- Speed: About 30 seconds
- Issues: Free version is limited to 25MB file size total. My 45MB set didn't work until I upgraded.
Verdict: Great tool, but the 25MB limit killed it for my needs.
Tool #3: PDF24 Tools (Online)
First Impression: Straightforward, no-frills interface
The Process: Upload files, rearrange if needed, merge.
Results:
- Output: 47.1MB (slightly larger than original)
- Quality: Good, though one graph looked slightly blurrier
- Speed: About 60 seconds
- Issues: None for free version. No daily limits I hit during testing.
Verdict: Solid choice. Not the fastest, but reliable and truly free.
Tool #4: Sejda PDF (Online)
First Impression: Professional-looking, lots of features visible
The Process: Upload, organize, merge. Interface was a bit cluttered but functional.
Results:
- Output: 41.9MB
- Quality: Excellent
- Speed: About 35 seconds
- Issues: Free version limits you to 3 tasks per hour and 200 pages per task. I exceeded the page limit.
Verdict: Good quality, but page limits are restrictive for larger projects.
Tool #5: Adobe Acrobat Online (Free Trial)
First Impression: Requires sign-in, which I hate, but interface is professional
The Process: Had to create an Adobe account first. Then upload and merge.
Results:
- Output: 43.8MB
- Quality: Perfect (as you'd expect from Adobe)
- Speed: About 40 seconds
- Issues: "Free" but really a trial. Kept pushing me to subscribe ($15/month).
Verdict: Best quality, but not really free. Only works if you're okay with the subscription model.
Tool #6: PDF Merge (Desktop App - Free)
First Impression: Had to download and install. Interface looked like it's from 2010.
The Process: Add files, arrange, click merge. Pretty basic.
Results:
- Output: 51.3MB (significantly larger)
- Quality: Fine, but file size bloat was concerning
- Speed: About 20 seconds (fastest so far)
- Issues: Tried to install browser extensions during setup. Had to decline carefully.
Verdict: Fast but file sizes balloon. Also sketchy installer behavior.
Tool #7: PDFtk (Command Line)
First Impression: For people who like terminal commands (so... not most people)
The Process: Had to look up the command syntax. Ran: pdftk file1.pdf file2.pdf ... output merged.pdf
Results:
- Output: 44.9MB
- Quality: Perfect
- Speed: About 15 seconds (very fast)
- Issues: You need to be comfortable with command line. Not user-friendly at all.
Verdict: If you know how to use it, it's incredibly powerful and fast. If you don't, look elsewhere.
Tool #8: Microsoft Edge "Print to PDF" Hack
First Impression: This is janky but I wanted to test it
The Process: Open first PDF in Edge, "Print," add more PDFs to print queue, save as PDF
Results:
- Output: Crashed on PDF #7
- Quality: N/A
- Speed: N/A
- Issues: Just didn't work for multiple large files
Verdict: Don't bother. Not designed for this use case.
Tool #9: Our Own TechLab247 Merger
First Impression: Okay I'm biased here, but I tested our own tool last
The Process: Upload files, automatic merging with optimization
Results:
- Output: 38.7MB (best compression while maintaining quality)
- Quality: Excellent
- Speed: About 35 seconds
- Issues: None in my testing
Verdict: Worked well. Files auto-delete after 24 hours which I appreciate from a privacy standpoint.
The Password-Protected PDF Problem
Remember I mentioned one of my test PDFs was password-protected? Most tools couldn't handle it.
Here's what happened:
- Smallpdf: Asked for the password, worked fine once I entered it
- iLovePDF: Same - prompted for password
- PDF24: Failed with an error
- Sejda: Prompted for password
- Adobe: Worked perfectly
- Desktop app: Failed
- PDFtk: Required me to decrypt first using a separate command
If you're merging protected PDFs, stick with tools that explicitly support password prompts.
File Size Surprises
One thing that shocked me: the variation in output file sizes.
Same 12 input PDFs (45MB total) produced outputs ranging from 38.7MB to 51.3MB depending on the tool.
Why? Different compression algorithms. Some tools optimize during merging (removing duplicate embedded fonts, optimizing images). Others just concatenate files without optimization.
If you're emailing the merged PDF, this matters. The difference between 39MB and 51MB could be the difference between "email sent" and "attachment too large error."
Quality Degradation Reality Check
I printed sample pages from each merged PDF to compare quality side-by-side.
Honestly? Most looked identical. I could only spot differences when I zoomed to 400% on screen or used a magnifying glass on the printouts.
The one exception was that sketchy desktop app, where some graphics looked noticeably softer.
For normal use - reading on screen, regular printing - any of the reputable online tools produced indistinguishable results.
The "Free" vs Actually Free Distinction
A lot of tools claim to be "free" but aren't really:
Free with limits: iLovePDF (25MB), Smallpdf (2 tasks/day), Sejda (200 pages)
Free trial: Adobe (wants subscription after)
Free with ads: Several desktop tools showed ads or tried to bundle other software
Actually free: PDF24, PDFtk, our tool
Know which category your tool falls into before committing to it for important work.
What I Actually Use Now
After all this testing, here's my current approach:
For quick one-off merges (under 25MB): Smallpdf - it's the fastest and easiest
For larger files or multiple merges: PDF24 or our own tool
For batch work or automation: PDFtk via command line
For absolute highest quality when I have budget: Adobe Acrobat
I keep bookmarks to 2-3 online tools because sometimes one is down or having issues.
Red Flags I Learned to Watch For
Requiring email sign-up before seeing results: Several tools did this. It's annoying and often means they'll spam you later.
Unclear file size limits: Some tools don't tell you about limits until AFTER you've uploaded and merged. Frustrating.
Suspiciously fast processing: If it seems too fast, it might not be actually processing - could just be concatenating without optimization.
No HTTPS: In 2024, any PDF tool not using HTTPS is suspicious. Don't upload sensitive documents.
Asking for unnecessary permissions: Desktop tools that want admin access or network permissions? Nope.
Practical Tips From My Testing
Test with non-sensitive files first: Before uploading your confidential client data to a random tool, test with some generic PDFs.
Check the output before sending: Always open the merged PDF and spot-check a few pages. I've caught issues that would have been embarrassing to send to clients.
Keep the originals: Don't delete your source PDFs until you've verified the merged version is good.
Consider your internet speed: Uploading 45MB to an online tool took me 2-3 minutes on my home WiFi. Factor this into your timeline.
Watch your privacy: Read the privacy policy. Some tools explicitly state they delete files after processing. Others don't mention it at all.
The One Thing Nobody Tells You
Page numbers.
When you merge PDFs, each original file might have its own page numbering. You might end up with three "page 1s" in your merged document.
Most free tools don't fix this. The merged PDF just has confusing page numbers.
If you need clean sequential numbering, you'll need either:
- Adobe Acrobat (can renumber pages)
- To add a cover page or table of contents
- To remove page numbers from source files before merging
I learned this when a client complained my merged report was "impossible to navigate." Whoops.
What I'd Do Differently
If I had to do this project again knowing what I know now:
I'd check the merged output before sending to the client. Found several issues AFTER the fact that would have been easy to fix beforehand.
I'd use a desktop tool for the final merge since I had all the files local anyway. Would have been faster than uploading 45MB.
I'd add a table of contents page so the three different page numbering schemes made sense.
Final Recommendations
Best all-around free tool: PDF24 Tools. No bullshit limits, good quality, reliable.
Best for ease of use: Smallpdf (if you're okay with the daily limit)
Best for power users: PDFtk command line
Best quality (paid): Adobe Acrobat Pro
Just avoid: Random desktop apps with sketchy installers
The honest truth is that most reputable online mergers produce nearly identical results. The main differences are in limits, speed, and file size optimization.
Pick one that fits your needs and stick with it. Having to learn a new interface every time you need to merge PDFs is more annoying than the actual merging.
