What is the smallest possible valid PDF? - pdf

Question

Out of simple curiosity, having seen the smallest GIF, what is the smallest possible valid PDF file?

Answer 1

This is an interesting problem. Taking it by the book, you can start off with this:
%PDF-1.0
1 0 obj<</Type/Catalog/Pages 2 0 R>>endobj 2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>endobj 3 0 obj<</Type/Page/MediaBox[0 0 3 3]>>endobj
xref
0 4
0000000000 65535 f
0000000010 00000 n
0000000053 00000 n
0000000102 00000 n
trailer<</Size 4/Root 1 0 R>>
startxref
149
%EOF
which is 291 bytes of PDF joy. Acrobat opens it, but it complains somewhat. There is one page in it and it is 3/72" square, the minimum allowed by the spec.
However, Acrobat X doesn't even bother with the cross reference table anymore, so we can take that out:
%PDF-1.0
1 0 obj<</Type/Catalog/Pages 2 0 R>>endobj 2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>endobj 3 0 obj<</Type/Page/MediaBox[0 0 3 3]>>endobj
trailer<</Size 4/Root 1 0 R>>
Acrobat complains, but opens it. Now we're at 178 bytes.
Turns out that you don't need that /Size in the trailer. Now we're at 172:
%PDF-1.0
1 0 obj<</Type/Catalog/Pages 2 0 R>>endobj 2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>endobj 3 0 obj<</Type/Page/MediaBox[0 0 3 3]>>endobj
trailer<</Root 1 0 R>>
Turns out you don't need all those pesky /Type elements in your dictionaries:
%PDF-1.0
1 0 obj<</Pages 2 0 R>>endobj 2 0 obj<</Kids[3 0 R]/Count 1>>endobj 3 0 obj<</MediaBox[0 0 3 3]>>endobj
trailer<</Root 1 0 R>>
Now we're at 138 bytes.
It also turns out that when the spec says "shall be an indirect reference" and /Count is required, and the header "must" be %PDF-1.0, they're making loose suggestions. This is the smallest I could make it and have it openable in Acrobat X:
%PDF-1.
trailer<</Root<</Pages<</Kids[<</MediaBox[0 0 3 3]>>]>>>>>>
70 bytes.
Now, my editor uses Windows newline discipline, but Acrobat accepts Windows, Mac, or Unix conventions, so by using a hex editor, I replaced the \r\n with \r and removed the last newline altogether, which leaves me with 67 bytes
25 50 44 46 2D 31 2E 0D 74 72 61 69 6C 65 72 3C
3C 2F 52 6F 6F 74 3C 3C 2F 50 61 67 65 73 3C 3C
2F 4B 69 64 73 5B 3C 3C 2F 4D 65 64 69 61 42 6F
78 5B 30 20 30 20 33 20 33 5D 3E 3E 5D 3E 3E 3E
3E 3E 3E
I tried taking off the last end dictionary (>>), but Acrobat wouldn't have that. The PDF reading built-in to Google Chrome (FoxIt) won't open it.
As a PostScript (HA! See what I did there?), if you consent to Acrobat "repairing" the file, it bumps up to 3550 bytes, most of it optional metadata, but it leaves behind a number of clear spec violations.

Answer 2

I could not get the hello world example to open.
For a small-ish file with text content :
%PDF-1.2
9 0 obj
<<
>>
stream
BT/ 9 Tf(Test)' ET
endstream
endobj
4 0 obj
<<
/Type /Page
/Parent 5 0 R
/Contents 9 0 R
>>
endobj
5 0 obj
<<
/Kids [4 0 R ]
/Count 1
/Type /Pages
/MediaBox [ 0 0 99 9 ]
>>
endobj
3 0 obj
<<
/Pages 5 0 R
/Type /Catalog
>>
endobj
trailer
<<
/Root 3 0 R
>>
%%EOF

Answer 3

Based on all the answers here, here's the smallest PDF with text:
SMALL_PDF = (
b"%PDF-1.2 \n"
b"9 0 obj\n<<\n>>\nstream\nBT/ 32 Tf( YOUR TEXT HERE )' ET\nendstream\nendobj\n"
b"4 0 obj\n<<\n/Type /Page\n/Parent 5 0 R\n/Contents 9 0 R\n>>\nendobj\n"
b"5 0 obj\n<<\n/Kids [4 0 R ]\n/Count 1\n/Type /Pages\n/MediaBox [ 0 0 250 50 ]\n>>\nendobj\n"
b"3 0 obj\n<<\n/Pages 5 0 R\n/Type /Catalog\n>>\nendobj\n"
b"trailer\n<<\n/Root 3 0 R\n>>\n"
b"%%EOF"
)
As base64. Copy this and test in Chrome:
data:application/pdf;base64,JVBERi0xLjIgCjkgMCBvYmoKPDwKPj4Kc3RyZWFtCkJULyAzMiBUZiggIFlPVVIgVEVYVCBIRVJFICAgKScgRVQKZW5kc3RyZWFtCmVuZG9iago0IDAgb2JqCjw8Ci9UeXBlIC9QYWdlCi9QYXJlbnQgNSAwIFIKL0NvbnRlbnRzIDkgMCBSCj4+CmVuZG9iago1IDAgb2JqCjw8Ci9LaWRzIFs0IDAgUiBdCi9Db3VudCAxCi9UeXBlIC9QYWdlcwovTWVkaWFCb3ggWyAwIDAgMjUwIDUwIF0KPj4KZW5kb2JqCjMgMCBvYmoKPDwKL1BhZ2VzIDUgMCBSCi9UeXBlIC9DYXRhbG9nCj4+CmVuZG9iagp0cmFpbGVyCjw8Ci9Sb290IDMgMCBSCj4+CiUlRU9G
To make the page bigger, adjust the MediaBox dimensions :)
/MediaBox [ 0 0 250 50 ]

Answer 4

I thought I'd make a smallest pdf that displays "Hello World". The text is in the lower left corner. Sorry about the 9-point font, any larger would cost an extra byte :)
172 bytes for Adobe Reader X (if saved with linefeed-only newlines and no trailing newline or null-byte):
%PDF-1.
1 0 obj<</Kids[<</Parent 1 0 R/Resources<<>>/Contents 2 0 R>>]>>endobj 2 0 obj<<>>stream
BT/ 9 Tf(Hello World)' ET
endstream
endobj trailer<</Root<</Pages 1 0 R>>>>
120 bytes for Chrome's builtin PDF viewer:
%PDF 1 0 obj<</Pages<</Kids[<</Contents<<>>stream
BT 9 Tf(Hello World)' ET endstream>>]>>>>endobj trailer<</Root 1 0 R>>
To easily see this in Chrome, paste this URI in the address bar (SO won't let me link to it, and it won't work at all in other browsers):
data:application/pdf,%25PDF%201%200%20obj%3C%3C%2FPages%3C%3C%2FKids%5B%3C%3C%2FContents%3C%3C%3E%3Estream%0ABT%209%20Tf(Hello%20World)'%20ET%20endstream%3E%3E%5D%3E%3E%3E%3Eendobj%20trailer%3C%3C%2FRoot%201%200%20R%3E%3E

Answer 5

I was going to give an example of what I thought was the minimal valid "universal" PDF. until I noticed that the whole ethos of using a PDF is to ensure it will render exactly the same on all devices and their PDF readers. However on cross checking my "perfectly small well formed PDF" I spotted this. TL;DR this is fixed in my personal minimal text template (at the end)
So the ground rule was "smallest possible valid PDF" but I consider this shortage should count as an invalid PDF since it does not adhere to the concept of "Fit for Purpose" thus the minimum PDF must itself as a minimum contain a minimum of one means of fixing a working font.
To explain my proposed solution and why its less than perfect here it is in a rough form because of cut and paste.
%PDF-1.0
%µ¶
1 0 obj
<</Type/Catalog/Pages 2 0 R>>
endobj
2 0 obj
<</Kids[3 0 R]/Count 1/Type/Pages/MediaBox[0 0 595 792]>>
endobj
3 0 obj
<</Type/Page/Parent 2 0 R/Contents 4 0 R/Resources<<>>>>
endobj
4 0 obj
<</Length 58>>
stream
q
BT
/ 96 Tf
1 0 0 1 36 684 Tm
(Hello World!) Tj
ET
Q
endstream
endobj
xref
0 5
0000000000 65536 f
0000000016 00000 n
0000000062 00000 n
0000000136 00000 n
0000000209 00000 n
trailer
<</Size 5/Root 1 0 R>>
startxref
316
%%EOF
Whilst not defined by the rules of the question I have included some past experience of user problems.
The first difference you might note is media box in 2nd obj is a hybrid MediaBox[0 0 595 792] which is a minimax A4 width and minimax US Letter high, since otherwise the "universal page" in most countries would force a second sheet # 100% scale printing either for too wide or too high a page definition for the locale defaults.
And the current problem is evidenced in 3rd obj as no fonts have been set for resources, thus in aiming for minimal the PDF, I contest without a font defined, will be Invalid.
Thus none of the answers so far including my own, appear to produce a PDF that will "WORK" as a "VALID" means to produce the same printout, regardless of platform or viewer.
Turning to libraries I found a 3MB zip with an exceptionally versatile windows.exe (a single file that can do most pdf functions like split merge import stamp export attachments etc.) which can take "Hello World! in a command line and produce a good working file, this is page centre zoomed in
it uses a stream for the text and its positioning, and has other conforming data like producer so I offer this as a potentially good minimal to pare down, note as presented this file will appear blank due to stream corruption from binary to text.
%PDF-1.7
%µ¶
1 0 obj
<</Pages 2 0 R/Type/Catalog>>
endobj
2 0 obj
<</Count 1/Kids[5 0 R]/MediaBox[0 0 595 792]/Type/Pages>>
endobj
3 0 obj
<</BaseFont/Helvetica/Encoding/WinAnsiEncoding/Subtype/Type1/Type/Font>>
endobj
4 0 obj
<</Filter/FlateDecode/Length 101>>
stream
xœ*Tp
QÐw3P04Ò30PISp
Q01
à˜kdf¢ga¬`bhâ%ç‚ô(„”#©Aîè"EéÚlA
HW‘‚†GjNN¾Bx~QNŠ¢¦BHÈÞ## ÿÿFå
endstream
endobj
5 0 obj
<</Contents 4 0 R/CropBox[0 0 595 792]/MediaBox[0 0 595 792]/Parent 2 0 R/Resources<</Font<</F0 3 0 R>>>>/Type/Page>>
endobj
6 0 obj
<</CreationDate(D:20220600600709+01'00')/ModDate(D:20220600600709+01'00')/Producer(me 2)>>
endobj
xref
0 7
0000000000 65536 f
0000000016 00000 n
0000000062 00000 n
0000000136 00000 n
0000000225 00000 n
0000000395 00000 n
0000000529 00000 n
trailer
<</Size 7/Info 6 0 R/Root 1 0 R/ID[<A2A0CE5CCD9D0DABD5845AD574BF0A5C><09BF9D281BE12CB5B5933BB2B62B0D4D>]>>
startxref
636
%%EOF
P.S I deliberately added a non valid item so is intentionally not the minimum working answer, see if you can work out what's clearly wrong:-)
My personal offering
So I am often asked how to write plain text templated PDFs thus need the font to be static (Helvetica or Courier should do) and a structure that is easy to modify using windows CMD line, so this suits my purpose its now 698 bytes as shown with two place holders to show multi-line so if needed can find and replace Helvetica with Courier (note intentional 2 spaces after to keep byte count)
%PDF-1.1
%âã
1 0 obj
<</Type/Catalog/Pages<</Type/Pages/Count 1/Kids[2 0 R]>>>>
endobj
2 0 obj
<</Type/Page/Parent 1 0 R/MediaBox[0 0 594 792]/Resources<</Font<</F1 3 0 R>>/ProcSet[/PDF/Text]>>/Contents 4 0 R>>
endobj
3 0 obj
<</Type/Font/Subtype/Type1/Name/F1/BaseFont/Helvetica>>
endobj
4 0 obj
<</Length 5 0 R>>
stream
BT
/F1 36 Tf
1 0 0 1 255 752 Tm
48 TL
( Hello)'
(World!)'
ET
endstream
endobj
5 0 obj
78
endobj
xref
0 6
0000000000 65536 f
0000000017 00000 n
0000000094 00000 n
0000000228 00000 n
0000000302 00000 n
0000000425 00000 n
trailer
<</Size 6/Info <</CreationDate(D:2023)/Producer(cmd2pdf)/Title(mini.pdf)>>/Root 1 0 R>>
startxref
446
%%EOF
To see how this approach works in windows command line RIGHT CLICK and download as text https://github.com/GitHubRulesOK/MyNotes/raw/master/MAKE-PDF.cmd (now 200 lines long!) NOTE browser security may ask you to trust a cmd as download thus use .txt extension and you will still need to change properties to UNBLOCK once you are happy it should do no harm to run it!
#mkl are you up for producing your best shot ?

Answer 6

According to this Ange Albertini lecture, the smallest possible valid PDF is 36 bytes:
%PDF-(NULL)trailer<</Root<</Pages<<>>>>>>
Where (NULL) is the unprintable ASCII 0 character.
However, as Ange notes, while this PDF is technically valid, most PDF reader apps will regard it as invalid based on the size alone, thus failing to open it.

Answer 7

I needed a PDF version which is usable by a PDF converter (A4 format issue.. all the above constructs worked with Adobe Reader and Chrome, but not with the PDF converter which required DIN A4).
I found this site and this PDF worked fine with the PDF converter I'm using: https://help.callassoftware.com/m/73261/l/798383-how-to-create-a-simple-pdf-file

Answer 8

Working for a PDF related company, I know that the following content will be working pretty well. This is a valid empty A4 page:
%PDF-1.4
%âãÏÓ
5 0 obj
<<
/Length 1
>>
stream
endstream
endobj
4 0 obj
<<
/Type /Page
/MediaBox [0 0 612 792]
/Resources <<
>>
/Contents 5 0 R
/Parent 2 0 R
>>
endobj
2 0 obj
<<
/Type /Pages
/Kids [4 0 R]
/Count 1
>>
endobj
1 0 obj
<<
/Type /Catalog
/Pages 2 0 R
>>
endobj
3 0 obj
<<
/Creator (PDF Creator http://www.pdf-tools.com)
/CreationDate (D:20150701112447+02'00')
/ModDate (D:20220607183602+02'00')
/Producer (3-Heights\222 PDF Optimization Shell 6.0.0.0 \(http://www.pdf-tools.com\))
>>
endobj
xref
0 6
0000000000 65535 f
0000000226 00000 n
0000000169 00000 n
0000000275 00000 n
0000000065 00000 n
0000000015 00000 n
trailer
<<
/Size 6
/Root 1 0 R
/Info 3 0 R
/ID [<1C3500CA9F7232B97E0EF3F789E8B7F2> <254C8D153F655D49945EAD68D801E011>]
>>
startxref
505
%%EOF
Now using Javascript, you can embed this into your js bundle. First encode in base64 the content above, then use the encoded string and create a Blob file with it by writing:
const str = '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';
const blob = new Blob([atob(str)], { type: 'application/pdf' });

Answer 9

In Java, use this:
private static String samplepdf = "255044462D312E0D747261696C65723C3C2F526F6F743C3C2F50616765733C3C2F4B6964735B3C3C2F4D65646961426F785B302030203320335D3E3E5D3E3E3E3E3E3E";
and then
byte[] bytes = hexStringToByteArray(samplepdf);
...
public byte[] hexStringToByteArray(String s) {
int len = s.length();
byte[] data = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+ Character.digit(s.charAt(i + 1), 16));
}
return data;
}