PDF m l operators - pdf

Question

I am using a PDF parser to extract lines from a pdf document. It fails on a specific doc generated pdf. The smallest pdf that it fails for has a 1 cell 1 row table, but the stream shows a 2 cell 1 row table. I have these questions:-
Why does the stream show 2 cells instead of just 1?
What are those re operators for, as there are no rectangles?
Who generates these instructions, is it MS Word? Or the PDF Printing application (Cute PDF Writer)?
Here is the pdf :-
Here is the relevant stream:-
stream
q 0.12 0 0 0.12 0 0 cm
/R7 gs
q
647 5996 m
700 5996 l
700 5885 l
647 5885 l
h
W n
0 0 0 rg
q
8.33333 0 0 8.33333 0 0 cm BT
/R8 11.04 Tf
0.998087 0 0 1 77.64 709.2 Tm
()Tj
ET
Q
Q
q
700 5996 m
746 5996 l
746 5885 l
700 5885 l
h
W n
0 0 0 rg
q
8.33333 0 0 8.33333 0 0 cm BT
/R8 11.04 Tf
0.998087 0 0 1 84 709.2 Tm
()Tj
ET
Q
Q
0 0 0 rg
600 5996 4 4 re
f
600 5996 4 4 re
f
604 5996 3892 4 re
f
4496 5996 4 4 re
f
4496 5996 4 4 re
f
600 5884 4 112 re
f
600 5880 4 4 re
f
600 5880 4 4 re
f
604 5880 3892 4 re
f
4496 5884 4 112 re
f
4496 5880 4 4 re
f
4496 5880 4 4 re
f
q
8.33333 0 0 8.33333 0 0 cm BT
/R8 11.04 Tf
0.998087 0 0 1 72 695.28 Tm
()Tj
ET
Q
Q
endstream
and here is the image drawn using the m and l instructions above :-

Answer 1

Why does the stream show 2 cells instead of just 1?
The stream does not show any cells at all. Only tagged PDFs may have a certain awareness of tables and table cells but your PDF does not look tagged.
What you (considering your question title) appear to mean are the sequences
647 5996 m
700 5996 l
700 5885 l
647 5885 l
h
W n
and
700 5996 m
746 5996 l
746 5885 l
700 5885 l
h
W n
But all they do is intersecting the current clip path with a rectangle. Thus, following drawing operations are restricted to the respective rectangle. Such restriction can be found in PDFs in many situations, table cells are only one of them, and such clip path changes are not even necessary for table cells...
Furthermore, considering the preceding transformation matrix change
0.12 0 0 0.12 0 0 cm
the rectangles above are fairly small, each probably large enough for a single character.
What are those re operators for, as there are no rectangles?
Well, they are rectangles.
Very small in height and/or width, but rectangles nonetheless.
And they are filled rectangles, cf. the f operator.
To make a long story short, the "lines" around the area we perceive as a table cell, are actually filled rectangles:
604 5996 3892 4 re
600 5884 4 112 re
604 5880 3892 4 re
4496 5884 4 112 re
Furthermore the corners of the cell are drawn as tiny squares (and each corner twice):
600 5996 4 4 re
600 5996 4 4 re
4496 5996 4 4 re
4496 5996 4 4 re
600 5880 4 4 re
600 5880 4 4 re
4496 5880 4 4 re
4496 5880 4 4 re
Thus, these re instructions give you the border edges and corners of what we perceive as table cell.
Who generates these instructions, is it MS Word? Or the PDF Printing application (Cute PDF Writer)?
The concrete instructions you see are PDF instructions. Thus, your printing application creates them.
Of course, though, your printing application creates them because that is how it interprets the MS Word output...

Answer 2

Cute PDF Writer apparently (from a quick glance on their web page) uses the Windows printing system. In general, in cases like this, you print from MS Word, and MS Word will try to use Windows methods to draw the lines and other items, which the printer driver (Cute PDF Writer in this case) will then translate to PDF commands. An intermediate stage with first rendering to PostScript and then translating to PDF is also possible.
So, that would mean that MS Word is responsible for the fact that two cells are drawn.
I only see one rectangle in the image of the PDF that you posted, so I'm not sure what is happening here. Also, I can't explain the other re commands. The rectangles in the second image look like they might be a frame around a two-on-one printed page, but the coordinates look strange, so it could also be something else.