# Merging PDF files

## Basic Example

```python
from pypdf import PdfWriter

merger = PdfWriter()

for pdf in ["file1.pdf", "file2.pdf", "file3.pdf"]:
    merger.append(pdf)

merger.write("merged-pdf.pdf")
merger.close()
```

For more details, see an excellent answer on
[StackOverflow](https://stackoverflow.com/questions/3444645/merge-pdf-files)
by Paul Rooney.

## Showing more merging options

```python
from pypdf import PdfWriter

merger = PdfWriter()

input1 = open("document1.pdf", "rb")
input2 = open("document2.pdf", "rb")
input3 = open("document3.pdf", "rb")

# add the first 3 pages of input1 document to output
merger.append(fileobj=input1, pages=(0, 3))

# insert the first page of input2 into the output beginning after the second page
merger.merge(position=2, fileobj=input2, pages=(0, 1))

# append entire input3 document to the end of the output document
merger.append(input3)

# Write to an output PDF document
output = open("document-output.pdf", "wb")
merger.write(output)

# Close File Descriptors
merger.close()
output.close()
```

## append
`append` has been slighlty extended in `PdfWriter`.

see [pdfWriter.append](../modules/PdfWriter.html#pypdf.PdfWriter.append) for more details

**parameters:**

*fileobj*: PdfReader or filename to merge
*outline_item*: string of a outline/bookmark pointing to the beginning of the inserted file.
                    if None, or omitted, no bookmark will be added.
*pages*: pages to merge ; you can also provide a list of pages to merge
             None(default) means  that the full document will be merged.
*import_outline*: import/ignore the pertinent outlines from the source (default True)
*excluded_fields*: list of keys to be ignored for the imported objects;
            if "/Annots" is part of the list, the annotation will be ignored
            if "/B" is part of the list, the articles will be ignored

examples:

`writer.append("source.pdf",(0,10))  # append the first 10 pages of source.pdf`

`writer.append(reader,"page 1 and 10",[0,9]) #append first and 10th page from reader and create an outline)`

During the merging, the relevant named destination will also imported.

If you want to insert pages in the middle of the destination, use merge (which provides (insert) position)

You can now insert the same page multiple times. You can also insert the same page many time at once with a list:

eg:
`writer.append(reader,[0,1,0,2,0])`
will insert the pages (1), (2), with page (0) before, in the middle and after

## add_page / insert_page
It is recommended to use `append` or `merge` instead

## Merging forms
When Merging forms, some form fields may have the same names, preventing access
to some data.

A grouping field should be added before adding the source PDF to prevent that.
The original fields will be identified by adding the group name.

For example, after calling `reader.add_form_topname("form1")`, the field
previously named "field1" will now identified as "form1.field1" when calling
`reader.get_form_text_fields(True)` or `reader.get_fields()`.

After that, you can append the input PDF completely or partially using
`writer.append` or `writer.merge`. If you insert a set of pages, only those
fields will be listed.

## reset_translation
During the cloning, if an object has been already cloned, it will not be cloned again,
    a pointer  this previously cloned object is returned. because of that, if you add/merge a page that has
    been already added, the same object will be added the second time. If later you modify any of these two page,
    both pages can be modified independantly.

To reset, call  `writer.reset_translation(reader)`

## Advanced cloning
In order to prevent side effect between pages/objects objects and all objects linked are linked during merging.

This process will be automatically applied if you use PdfWriter.append/merge/add_page/insert_page.
If you want to clone an object before attaching it "manually", use clone function of any PdfObject:
eg:

`cloned_object = object.clone(writer)`

if you try clone an object already belonging to writer, it will return the same object

`cloned_object == object.clone(writer)  # -> returns True`

the same, if you try to clone twice an object it will return the previously cloned object

`object.clone(writer) == object.clone(writer)  # -> returns True`

Also, note that if you clone an object, you will clone all the objects below
including the objects pointed by IndirectObject. because of that if you clone
a page that includes some articles ("/B"),
not only the first article, but also all the chained articles, and the pages
where those articles can be read will be copied.
It means that you may copy lots of objects, that will be saved in the output pdf.

In order to prevent, that you can provide the list of defined the fields in the dictionaries to be ignored:

eg:
`new_page  = writer.add_page(reader.pages[0],excluded_fields=["/B"])`
