How to print or cat text into pdf() in R without markdown

Question

I'm creating a PDF file with some plots, but I want to also include some text message at the bottom. For reasons beyond my control, I cannot install a latex distribution on this system, so I can't knit a markdown file, but have to use pdf().

When I just use print or cat nothing shows up in the pdf. I tried using sink() based on the answer from here, but that didn't work either:

pdf("filename.pdf")
sink("filename.pdf")
print("message")
sink()
dev.off()

No error message was received, but the file created has no pages.

Any ideas? I'm considering a workaround of just plotting a text only plot, but I'm hoping there's a more reasonable solution.

Answer 1

I had success solving this problem (PDFs only and R/RStudio but not RMarkdown) by using the package qpdf, specifically the pdf_overlay_stamp() function.

#Set WD
setwd("INSERT PATH FOR DESIRED INPUT FILES AND OUTPUT FILE")

#Generate Sample Files
pdf("Part1.pdf", width = 8.5, height = 11)
plot.new()
text(x = 0.35, y = 1, adj = c(0,1), labels = "This is Part1.pdf")
dev.off()

pdf("Part2.pdf", width = 8.5, height = 11)
plot.new()
text(x = 0.35, y = 0.5, adj = c(0,1), labels = "This is Part2.pdf")
dev.off()

#Identify files to overlay
f1 <- "Part1.pdf"
f2 <- "Part2.pdf"

#Overlay Text
qpdf::pdf_overlay_stamp(input = f1, stamp = f2)

If you already have source PDFs just substitute f1 and f2 for the file names of the base file and the stamp/watermark that you wish to overlay onto the base file.

Please note that pdf_overlay_stamp() pulls all pages from the f1/input file but only the 1st page from f2/stamp file.

You will need to change the x and y values for the plot for the "Part1.pdf" to change the placement of your desired text.

Answer 2

We simply could plot the text with text in pdf device. text only works after a plot call. That we don't have to deactivate everything, we call plot.new which is basically an empty plot. Look into ?pdf and ?text options for further customizing.

txt <- "message"

pdf("filename2.pdf", paper="a4")
plot.new()
text(x=.1, y=.1, txt)  # first 2 numbers are xy-coordinates within [0, 1]
text(.5, .5, txt, font=2, cex=1.5)
text(.9, .9, txt, font=4, cex=2, col="#F48024")
dev.off()

For the sink solution rather use cat and add a carriage return \r at the very end of the text to obtain a valid last line for pdf processing of the .txt file.

sink("filename.txt")  # to be found in dir `getwd()`
cat("message\r")
sink()

pdf("filename.pdf")  # ditto
plot.new()
text(.5, .5, readLines("filename.txt"))
dev.off()

Customize with different x and y coordinates, font options, and paper formatting in pdf call.

Result