Combine multiple PDF files into one document

Question

I have multiple single page PDFs I'd like to join together into a single file. (Obviously I mean the file format and not the probability distributions here!)

I'm aware of free online services such as this one and I have used them several times. On this occasion, however, I have info I'd prefer not to upload to a server I don't know anything about.

I know Mathematica can Import and Export PDFs, but is there any easy way to join them together? I've tried using Join, but it produces a single large page instead of a page 1, page 2, page 3 format. Also the file size balloons - joining a 500 kB and 208 kB pdf results in a 3,503 kB file.

Answer 1

Update

As @VCL pointed out in his comment, just exporting a list of graphics does not work since the braces and commas of the list a exported as well. Additionally, the pdf is one single page. Here is an updated approach, which takes all imported pdf-pages and inserts them into a new notebook where every page is separated by a pagebreak.

The resulting pdf has at least several pages, but content of the page is scaled and (if not turned off) the headers are printed too into the pdf.

First, we simply import the "Pages" from a file

pages = 
  Import["http://amath.colorado.edu/documentation/LaTeX/Symbols.pdf", "Pages"];

Now we try to make a new pdf which has the original file appended to itself. For this I join the pages together, riffle a newline-cell between them and create a new notebook which is instantly exported into a pdf-file:

Export["tmp/test.pdf", 
 CreateDocument[
    Riffle[Join[pages,pages], Cell["", "PageBreak", PageBreakBelow -> True]
 ], Visible -> False]
]

This works here (MacOSX) but when you look closer at the created pdf, you see things like

while in the original document this was type-set properly

Not to forget, that the resulting pdf is much bigger than two copies of the original file would have been! Input pdf file size: 256K, Mma output: 3.2MB, gs output: 176kB.

Answer 2

For merging PDF files one can use the PyMuPdf library for Python as shown here.

First, install PyMuPdf (it requires Python 3.6 or later):

python -m pip install --upgrade pip
python -m pip install --upgrade pymupdf

Define mergePDFs via ExternalFunction:

mergePDFs = ExternalFunction["Python", "import fitz
def merge_pdfs(sources, output):
    result = fitz.open()
    for pdf in sources:
        with fitz.open(pdf) as mfile:
            result.insert_pdf(mfile)
    result.save(output)
    return output"]

It can be used as follows:

SetDirectory[$UserDocumentsDirectory];
mergePDFs[DeleteCases[FileNames["*.pdf"], "result.pdf"], "result.pdf"]

"result.pdf"

It works extremely fast. For example, merging 505 PDF files takes only about 0.7 seconds on my laptop producing a PDF of size 11 MB.

_{P.S. There is a limitation due to a bug in the current (1.19.4) version of PyMuPdf: it can merge no more than 508 files at one call and cannot merge into one of the source files (fixed in version 1.19.5).}

---

Here is an example of what we can get with this function:

plots = {Plot[{Sin[x], Sin[2 x], Sin[3 x]}, {x, 0, 2 Pi}, PlotLegends -> "Expressions"],
   Plot[{Sin[x], Sin[2 x], Sin[3 x]}, {x, 0, 10}, PlotLayout -> "Column"],
   Plot[{BesselJ[0, x], BesselJ[1, x], BesselJ[2, x], BesselJ[3, x], BesselJ[4, x], 
     BesselJ[5, x]}, {x, -20, 20}, PlotLayout -> {"Column", UpTo[4]}]};
tempFiles = 
  Table[Export[StringTemplate["~temp~``.pdf"][i], plots[[i]]], {i, 1, Length[plots]}];
If[mergePDFs[tempFiles, "plots.pdf"] === "plots.pdf", 
  DeleteFile@tempFiles; "plots.pdf", $Failed] // SystemOpen