What is the file encoding method being used here?

Question

Binary files are frequently attached to SEC filings (see example here) and I am writing a parser to capture this text and re-create the file.

It doesn't matter if the file is an Excel spreadsheet or PDF (which is the sample below and linked to), the encoding method looks the same. Its not Base64; I don't recognize it.

Do you? TIA.

<DOCUMENT>
<TYPE>LETTER
<SEQUENCE>1
<FILENAME>filename1.pdf
<TEXT>
<PDF>
begin 644 filename1.pdf
M)5!$1BTQ+C4-)>+CS],-"C,W(#`@;V)J#3P\+TQI;F5A<FEZ960@,2],(#$T
M-C0S,2]/(#,Y+T4@,30Q-S0W+TX@,2]4(#$T-C$R,R]((%L@-#8X(#$V,ET^
M/@UE;F1O8FH-("`@("`@("`@("`@("`@#0HT-R`P(&]B:@T\/"]$96-O9&50
M87)M<SP\+T-O;'5M;G,@-2]0<F5D:6-T;W(@,3(^/B]&:6QT97(O1FQA=&5$
M96-O9&4O241;/#`T-#$S,4$Q.#`Q-D,X-#!!-S$X0S-%,T$X1D5$0S!!/CQ!
M,31&,S%#,T(Y-T(T-#0P.3)"-#<P148U,D8W0C,X13Y=+TEN9&5X6S,W(#,R
....
...<snip>...
....
M``$F1B;-S0Q,#`S,"2"2-PU$,O:!2(:C0-E_QTS!;`;&H4$R/0&1C`P``08`
M_(\&40T*96YD<W1R96%M#65N9&]B:@US=&%R='AR968-"C$Q-@T*)25%3T8-
!"C\_
`
end
</PDF>
</TEXT>
</DOCUMENT>

Answer 1

The answer turned out to be old school: UUEncoding

Thanks to all who viewed the question.