I have a PDF file broken up and extracted in many different packets how can I reassemble and restore the file?

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As the "splittig" procedure does not add extra characters nor remove any of them, to reassemble the packets is sufficient to join the packets in the original order, and I assume they have been numbered sequentially.
To do that, any method capable of joining packets is good.
You can use a Ms-Dos command (copy /b file1+file2+.....+fileN Output.pdf), or a public domain tool like WGet (wget -i list.txt -O output.pdf), where in list.txt you put the names of all the files to assemble, just use the straight slash, or even an Excel Vba program, as in the following example:
const prefix="seg-"
const suffix=".ts"
const fileout="output.pdf"
dim i as integer
dim s as string
open fileout for binary as 1
for i=1 to 900
open prefix & i & suffix for binary as 2
s = Input(LOF(2), 2)
put 1,,s
close 2
next
close #1
Obviously, you have to fine tune the names to your situation, specially to account for the numeric part of the packet name, if it is fixed length or variable length.
I hope this helps.